Ukraine's defence minister has said its forces have restored control of the border with Russia and can now prevent military equipment being brought across the frontier, as a second successive day of fighting continued in the east.
"Our forces have completed the encirclement of the problem region and restored the state border of Ukraine. Last week we fully closed off the possibility of any military equipment being brought in from the Russian Federation," acting Defence Minister Mykhailo Koval said.
President Vladimir Putin's top foreign policy adviser denied on Friday that Russia was building up troops on the frontier but said it had brought in more border guards because of security concerns, Reuters news agency reported.
Dismissing remarks by NATO Secretary-General Anders Fogh Rasmussen that at least a few thousand more Russian troops were now at the border, Kremlin adviser Yuri Ushakov said: "There has been no buildup."
Fighting between government forces and pro-Russian rebels raged again on Friday with reports of losses on both sides.
Vladislav Seleznyov, spokesman for Kiev's forces in the east, said on Friday that seven soldiers were killed and 30 injured in overnight fighting against pro-Russian separatists outside the village of Yampil in the Donetsk region that started the day before.
Seleznyov said about 300 separatists had been killed in clashes around the villages of Yampil and Zakitne which included artillery fire and air attacks.
The casualty figures for the pro-Russian separatists could not be independently confirmed, though a rebel commander said on Thursday that the rebels had sustained "heavy losses" when they were outgunned by government forces backed by heavy armour, Reuters news agency reported.
Friday's fighting took place about 100kms from the border with Russia. It comes a day after NATO reported that Russia was resuming a military build-up at the Ukrainian border.
Heavy weapons were seized from the separatists, including an armoured personnel carrier, a truck with a high-calibre machine gun mounted on it, a shoulder-fired missile, grenade launchers and small arms, Seleznyov said in a Facebook post.
Fighting broke out east of the town of Krasny Liman early on Thursday after pro-Russian separatists refused to lay down their weapons in line with a peace plan proposed by Poroshenko, government forces said.
Putin and Poroshenko discussed details of the peace plan in a telephone call on Thursday, the Associated Press news agency reported.
Poroshenko's office said he emphasised the need for introducing effective border controls and quickly releasing hostages.