Washington: The White House has urged Moscow to stop its "extremely dangerous and provocative" attempts to destabilise Ukraine, where tensions have soared again.
There has been an "escalation" in Russian activity in recent weeks to unsettle the already tense situation on the ground in eastern Ukraine, National Security Council spokeswoman Caitlin Hayden said in a statement on Friday.
NATO and Ukraine said a column of military vehicles crossed into Ukraine from Russia on Thursday night and most of them had been destroyed by Ukrainian artillery fire. It was not clear whether Russian soldiers or rebel separatists were driving the vehicles.
Ukraine's President Petro Poroshenko was quoted in a statement on his website he could confirm some Western news reports the column had crossed into Ukraine.
"The President informed that the given information was trustworthy and confirmed because the majority of the machines had been eliminated by Ukrainian artillery at night," the statement said.
In Copenhagen, NATO Secretary-General Anders Fogh Rasmussen said the alliance had detected an "incursion" of vehicles from Russia.
Meanwhile, the convoy of more than 260 trucks that Russia says are filled with food and other aid for civilians caught up in the fighting in eastern Ukraine remained stalled inside Russia on Friday amid confusion over when inspections would start. Ukraine and its Western allies want to ensure the cargo contains only relief supplies and not items that could help pro-Russian fighters battling to survive a Ukrainian offensive.
A statement on Friday by the Ukrainian military said border guards had started examining the trucks, but the military's spokesman Andriy Lysenko later denied this and said inspections could not begin until the Ukrainian authorities received documents detailing the trucks' contents.
Mr Lysenko said Ukraine had sent border guards and customs officials to a Russian border town to examine the trucks but was still waiting for the necessary documentation from the International Committee of the Red Cross. The Red Cross, for its part, said Russia had yet to provide a detailed inventory and called for a speedy resolution of the problem.
In a statement issued in Geneva, the Red Cross said swift action was needed to allow "confirmation of the strictly humanitarian nature of the cargo".
Referring to the claimed partial destruction of the Russian armoured column, Ms Hayden said: "Even as we work to gather information, we reiterate our concern about repeated Russian and Russian-supported incursions into Ukraine. Russia has no right to send vehicles, persons or cargo of any kind into Ukraine, under any pretext, without the government of Ukraine's permission."
She warned "the escalation in Russian activity designed to destabilise Ukraine in recent weeks is extremely dangerous and provocative. It includes supplying separatist fighters with tanks, armoured vehicles, artillery and multiple-rocket launchers."
Russia has also been firing artillery and rockets from Russian territory into Ukraine "on a regular basis," Ms Hayden said.
Moscow has consistently denied supporting rebels in eastern Ukraine and the crisis has led to tit-for-tat sanctions between the West and Russia over Moscow's alleged behaviour.
Russian President Vladimir Putin can help put a stop to the conflict "by ending Russian firing into Ukraine; stopping its supply of weapons, support and cash to separatists; and closing the border to militants, including by facilitating an effective border monitoring mission under the auspices of the OSCE [Organisation for Security and Co-operation in Europe]," Ms Hayden said.
"The continued Russian military intervention into Ukraine is entirely at odds with legitimate efforts to provide humanitarian assistance and negotiate a peaceful resolution to the overall crisis."
AFP, New York Times