The US and Germany have denounced the movement of a Russian aid convoy into Ukraine without permission from Kiev, calling on Moscow to stop dangerous escalations in its neighbour country.
US President Barack Obama and German Chancellor Angela Merkel have discusses the Ukraine crisis over the phone on Friday, according to a White House statement.
Both leaders believe that the presence of Russian soldiers in Ukraine, the build-up of Russian troops along the Ukrainian border and Russian shelling into Ukraine represent dangerous escalations of tensions by Moscow, the White House said.
It also said the two leaders agreed that a Russian convoy that entered Ukraine without approval is yet another provocation by Moscow that violates Ukraine's sovereignty.
Obama and Merkel agree that Russia must remove the convoy and withdraw from Ukrainian territory, the statement said.
Mark Lyall Grant, British ambassador to the UN, also called Russia's aid convoy "an undeniable and blatant violation of Ukrainian sovereignty" after a closed-door meeting of the UN Security Council. Grant said Moscow had no support in the council for its action, an assertion the Russian ambassador denies.
Moscow rejects allegations
Russia says the convoy that entered Ukraine on Friday is for humanitarian purposes, but Ukraine and the US say the Russians failed to abide by conditions set by Ukraine and the International Red Cross.
Vitaly Churkin, Russia's UN ambassador, said that Moscow "waited long enough and it was time to move".
"At times it seems there is no clear chain of command in Kiev, because some assurances are given [to Russia] at a very high level and then others do not give the orders which are required ... by the border police to let the [aid] trucks in," Churkin said. "That game could not continue indefinitely."
Ukraine's state security chief said the move amounted to a "direct invasion" by Russia.
"We consider this a direct invasion by Russia of Ukraine," Valentyn Nalivaychenko, Ukraine's state security chief, told journalists, according to the Reuters news agency.
He added that Ukraine would not use force against the convoy "to avoid provocations".
At least 90 trucks crossed the border into eastern Ukraine on Friday, Reuters reported. It was thought they were escorted by pro-Kremlin separatists and later entered Luhansk.
The trucks were loaded with water, generators and sleeping bags intended for civilians of the besieged city, where pro-Russian separatist fighters are besieged by Ukrainian forces.
More than 200 trucks had been held at the border zone over Ukraine's concerns that Russia had not complied with International Red Cross rules regarding humanitarian aid.
Several of the vehicles had been cleared by both countries' customs authorities on Thursday and were waiting for the green light to enter Ukraine from an ICRC team that had been overseeing the operation.
Ukraine has expressed repeated fears that Russia may be using the vehicles to smuggle in weapons to pro-Kremlin rebels who have been battling government forces for more than four months.
Russia has consistently denied that it is arming separatist rebel groups operating in the eastern cities of Luhansk and Donetsk.