Ukraine: 5 die as government forces clash with pro-RussiansKIEV, Ukraine (CNN) -- Ukrainian forces killed five militants during operations to take down pro-Russians' roadblocks in Slavyansk on Thursday, the Ukrainian Interior Ministry said, in what appeared to be a significant escalation of violence in the country.
By: Ben Brumfield, Laura Smith-Spark and Victoria Butenko, CNN, CNN
KIEV, Ukraine (CNN) -- Ukrainian forces killed five militants during operations to take down pro-Russians' roadblocks in Slavyansk on Thursday, the Ukrainian Interior Ministry said, in what appeared to be a significant escalation of violence in the country.
At the same time, Russia and the West continued their war of words over the handling of the crisis.
Russian President Vladimir Putin said that if the Kiev government "has started to use the army against the population inside the country, it, beyond any doubt, is a very serious crime."
This would "have consequences" for those making the decisions, and for relations between the two governments, Putin said at a media forum Thursday, according to Russian state TV channel Russia 24.
Shortly afterward, Russian Defense Minister Sergei Shoigu said Russia would conduct military drills in response to the operation in southeastern Ukraine, Russian state news agency RIA Novosti said.
"We are forced to react to such a development in the situation," Shoigu is quoted as saying. "Starting today, exercises of battalion tactical groups from the Southern and Western military districts will begin near the borders with Ukraine."
NATO and the United States have already voiced unease about an estimated 40,000 Russian troops gathered near the Ukrainian border.
Conflicting accounts have emerged about the number of casualties resulting from clashes Thursday.
The government in Kiev confirmed operations to destroy three checkpoints around Slavyansk and said its forces killed five pro-Russian militants. A police officer was also injured, the Interior Ministry said.
Meanwhile, Stella Horosheva, a spokeswoman for the self-appointed pro-Russian mayor of Slavyansk, Vyacheslav Ponomaryov, said an attack at an impromptu roadway checkpoint outside the city had taken the life of one pro-Russian militiaman and wounded another.
The pro-Russian unit at the checkpoint told a CNN team that armored vehicles had come to the roadblock but had refused to shoot at people, and that locals had set fire to tires to prevent them from passing.
The unit said two members of the "self-defense" group were on their way home after an overnight stint at the barricade when a sniper killed one and injured another.
Ponomaryov, visiting the site, also said a sniper had killed one of the pro-Russian activists.
The Interior Ministry said leaflets had been distributed "which called on people to keep the peace, not leave their residences, to keep children inside, to not react to provocation and to not obey illegal orders issued by the self-proclaimed illegal authorities."
The government accused Ponomaryov of threatening to kill anyone possessing the leaflet.
Reports of threats against Slavyansk residents have not been independently confirmed by CNN.
Elsewhere in the eastern Donetsk region, where some pro-Russian protesters have tried to declare independence from Ukraine, gunmen opened fire on a Ukrainian military unit overnight.
One Ukrainian soldier was injured in the assault in the town of Artemivsk, Ukraine's Defense Ministry said Thursday.
But security forces fought off the attack and retained control of the facility, the ministry said.
Interior Minister Arsen Avakov on his Facebook page accused the group of roughly 70 attackers of trying to take weapons from the unit.
Crossed claims in Mariupol
Both the government and pro-Russian protesters claimed victory in the eastern city of Mariupol on Thursday.
Acting President Oleksandr Turchynov opened a meeting of parliament with the announcement that the city hall, which pro-Russian protesters had occupied, had been freed.
Avakov said on his Facebook page that there were no casualties in the operation and that the Interior Ministry was preparing the premises for employees to return to work.
But pro-Russian protester Irina Voropayeva, who is in Mariupol, contradicted them both.
An assault on the city hall failed to dislodge the protesters, she said. Some of the occupiers were injured while they fought off the attackers, whom she said were extreme-right Ukrainian toughs.
The Ukrainian Interior Ministry later revised its version of events in a post to its website.
A group of 30 people armed with baseball bats entered city hall early Thursday and demanded the occupiers leave, it said. As the two groups clashed, police tried to separate them. Five people were injured.
Obama: U.S. 'teed up' to impose more sanctions
A week ago, the United States, Russia, the European Union and Ukraine sat down in Geneva, Switzerland, to hammer out an agreement calling for illegal groups to disarm and vacate occupied buildings, in return for an amnesty.
It has seemingly gone ignored, as the rift between the parties involved grows and Russia and the West accuse each other of foiling the agreement by meddling in Ukraine's affairs.
On Thursday, U.S. and Russian leaders exchanged new barbs.
Speaking alongside Japanese Prime Minister Shinzo Abe in Tokyo, U.S. President Barack Obama again ruled out any military solution in Ukraine but warned that the United States is "teed up" to impose further sanctions on Russia if it does not abide by the April 17 deal.
"There was some possibility that Russia could take the wiser course after the meetings in Geneva," he said. "Instead, we continue to see militias and armed men taking over buildings, harassing folks who are disagreeing with them, and destabilizing the region, and we haven't seen Russia step up and discourage that.
"On the other side, you've seen the government in Kiev take very concrete steps, in introducing an amnesty law and offering a whole range of reforms with respect to the constitution, that are consistent with what was discussed in Geneva."
But Russia sees things very differently, saying that according to the Geneva deal, Kiev must act to disarm the right-wing ultranationalists that Moscow blames for violence in Ukraine.
"We don't have any doubts that the first step must be done by the Kiev authorities," Russian Foreign Minister Sergey Lavrov said at a news conference Thursday.
He accused the West of treating leaders in Kiev like "angels" who did nothing wrong while blaming Russia for the unrest in eastern Ukraine.
Lavrov also charged the European Union and the United States with supporting an "anti-constitutional coup" in Ukraine.
Putin, speaking on Russia 24, said the events unfolding in eastern Ukraine demonstrate that Moscow's decision to support the Crimean people, who voted to join Russia last month in a referendum condemned by the West, was right.
"Otherwise they would have witnessed the same events as eastern Ukraine and surely even worse," he said. "So, this is another proof that we have acted correctly and on time."
Former U.S. Secretary of State Hillary Clinton reproached Putin over Ukraine while speaking at the University of Connecticut on Wednesday.
She accused him of "trying to turn the clock back to the Soviet Union days."
"I think Russia will pay a big price for this," she said.
The West has alleged that Moscow sent members of its armed forces into the country, providing other support for pro-Russian militants or generally contributing to an atmosphere of distrust and instability.
Some in the West fear that Russia will try to repeat its annexation of Crimea elsewhere in Ukraine and perhaps in other countries in which ethnic Russians live or where Russia or the former Soviet Union historically has had significant influence.
Clinton called for keeping Ukraine's territory intact and allowing it to have a relationship with the West.
Lavrov threw the allegation back at the United States this week.
"(Americans) have, I think, overwhelming influence," he said. "They act in a much more open way, without any scruples, compared to the Europeans. ... You cannot avoid the impression that they are running the show very much, very much."
As proof, Lavrov pointed to the timing of the Ukrainian government's relaunch of its security operation just after a two-day visit from U.S. Vice President Joe Biden.
He claimed Turchynov has "ordered the army to shoot at ... people if they are engaged in peaceful protests," yet hasn't disarmed extremists.
On the other hand, pro-Russian protesters have not left government buildings they have seized or disarmed, as was mandated by the Geneva agreement.
Meanwhile, NATO estimates that Russia has amassed 40,000 troops near its border with Ukraine. This has fueled speculation the conflict could only get bigger and more violent, with Russia possibly taking over some, if not all, of Ukraine and possibly neighboring nations.
Lavrov didn't say on Wednesday that any military intervention was imminent, but he didn't rule it out, either.
"Russian citizens being attacked is an attack against the Russian Federation," he said.
A company-size contingent of U.S. Army paratroopers arrived Wednesday in Poland for training exercises, at Warsaw's request.
The contingent is part of "a persistent rotational presence," said Pentagon spokesman Rear Adm. John Kirby.
The United States and its allies have accused Russia of fomenting unrest in Ukraine since massive demonstrations helped push out pro-Russian President Viktor Yanukovych, who came under fire for shifting Ukraine away from the European Union and closer to Moscow.
CNN's Victoria Butenko reported from Kiev; CNN's Ben Brumfield wrote and reported from Atlanta and Laura Smith-Spark from London. CNN's Alla Eshchenko and Tim Lister reported from near Slavyansk and Gul Tuysuz from Kiev. CNN's Arkady Irshenko, Boriana Milanova and Gabe LaMonica contributed to this report.