It came as Russia’s foreign minister Sergei Lavrov reiterated to the German foreign minister in a phone call that Ukraine’s use of the army must be halted in its country.
Earlier Mr Lavrov had warned Kiev that it would face justice for a "bloody crime" in eastern Ukraine, where the government has been acting against rebels.
"They (Kiev) are waging a war on their own people. This is a bloody crime, and those who pushed the army to do that will pay, I am sure, and will face justice," Mr Lavrov told a meeting of diplomats.
The massing of Russia’s forces on its border prompted Ukrainian Prime Minister Arseniy Yatsenyuk to accuse Russia of wanting to start "a third world war".
Mr Yatsenyuk said that Russia wanted to occupy Ukraine, creating a conflict that would spread to the rest of Europe.
He said: "The world has not yet forgotten the second world war, but Russia is already keen on starting a third world war."
"All responsibility for aggression on Ukrainian territory and for undermining international security and stability rests with the leadership of the Russian Federation."
On the ground, Ukrainian special forces launched a second phase of their "anti-terrorism" operation, blockading the rebel-held city of Slavyansk.
Reports that pro-Russian snipers had shot at a Ukranian military helicopter in the eastern town of Kramatorsk have been treated cautiously.
According to officials in Kiev, the helicopter exploded at a military base after being hit by a rocket-propelled grenade.
Sky's Foreign Affairs Editor Sam Kiley, in Ukraine, said that the "bellicose" rhetoric between Russia and Ukraine was escalating more quickly than action on the ground.
He said suggestions that residents allied to Russia were being intimidated were not true.
Pro-Moscow rebels holding the flashpoint town of Slavyansk vowed on Friday they would never give up.
"We will not surrender the town," their leader Vyacheslav Ponomaryov told a news conference.
"We will resist as long as possible. The town is blockaded. We are ready to defend it."
Ukrainian authorities, who sent the army into Slavyansk on Thursday in a brief incursion that killed one militant, said on Friday they were encircling the town to prevent rebel reinforcements arriving.
Mr Ponomaryov, self-styled unelected mayor of the town, has publicly called for Russian troops to be deployed to the area as "peacekeepers".
Meanwhile, US journalist Simon Ostrovsky, who was captured and released by pro-Russian militants, says he believes he was used as a "bargaining chip" with Kiev after his abduction.
Writing for Vice magazine, he said: "After spending hours alone on the floor of a damp cell … I was led into a room where I was accused of working for the CIA, FBI, and Right Sector, the Ukrainian ultra-nationalist group."
UN chief Ban Ki-moon has warned that the crisis is threatening to "spin out of control" and urged all sides to "refrain from violence".
Source: Sky News