MOSCOW — Russia is resuming its military buildup along the Ukrainian border in an apparent attempt to intimidate its neighbor, NATO's chief said Thursday as Ukrainian government forces unleashed a major offensive against pro-Moscow insurgents.
Russian President Vladimir Putin spoke by telephone to German Chancellor Angela Merkel and French President Francois Hollande, voicing strong concern about the Ukrainian military onslaught. Putin said he expects Ukrainian President Petro Poroshenko to immediately launch his plan to end the violence, the Kremlin said.
Putin and Poroshenko then discussed details of the peace plan in a phone call — their second conversation this week. Poroshenko's office said he emphasized the need for introducing effective border controls and quickly releasing hostages.
Russia has denied Ukrainian and Western allegations that it is fomenting the rebellion by sending troops and weapons into Ukraine.
Last month, in an apparent attempt to ease tensions in Ukraine, Putin pulled back many of the estimated 40,000 Russian troops massed along the border.
But on Thursday, NATO Secretary General Anders Fogh Rasmussen said that Russia has sent a few thousand additional troops to the border, calling it "a very regrettable step backward."
"If they're deployed to seal the border and stop the flow of weapons and fighters, that would be a positive step. But that's not what we're seeing," Rasmussen said in London.
The Russian Defense Ministry refused to comment.
The allegations came as heavy fighting raged near Krasnyi Liman in the Donetsk region, which has been the epicenter of violence over the past two months.
Vladislav Seleznev, a spokesman for Ukrainian forces in the east, described the area as a strategic supply corridor for the rebels. He said in a statement on Facebook that four government troops were killed and 20 wounded in the fighting Thursday.
He said up to 200 rebels were killed and hundreds wounded. The claim could not be independently confirmed.
Rebel chief Igor Strelkov said in a statement on YouTube that his men were far outnumbered and outgunned and would probably be forced to retreat.
Strelkov, clad in combat fatigues, bitterly scolded the Kremlin for failing to help the rebellion and issued a desperate plea to send in troops.
"I hope that they have enough conscience left in Moscow to take some measures," he said.
There was no immediate response from the Kremlin, which has ignored previous pleas for help from the insurgents.
Putin has faced strong pressure from nationalists at home to send troops into Ukraine following the annexation of Crimea in March.
But Putin, eager to avoid a new round of crippling Western sanctions, has instead welcomed a peace plan put forward by Ukraine's new president.
Poroshenko on Wednesday promised to call a unilateral cease-fire to give the rebels a chance to lay down their weapons and leave the country. He is expected to outline details of the plan Friday.
The new Russian military deployments come at a delicate time.
Next week, the foreign ministers and leaders of the European Union are scheduled to meet and could consider tougher economic sanctions against Russia over the Ukraine crisis.
"The international community would have to respond firmly if Russia were to intervene further," Rasmussen said. "That would imply deeper sanctions."