BRUSSELS - NATO's top military commander accused Russia on Wednesday of destabilizing eastern Ukraine through the use of Russian-backed forces and demanded that it stop interfering.
While a majority of the troops Russia had close to the Ukrainian border - previously estimated by NATO at 40,000 - had withdrawn or were in the process of withdrawing, some appeared intent on staying, US Air Force General Philip Breedlove, NATO's supreme allied commander Europe, said.
"There are several large formations that are remaining and they have not reduced their presence in any way. Some portion of the force looks like it intends to remain," he said.
Breedlove said he saw Russia's hand behind unrest in eastern Ukraine, where pro-Russian separatists have seized control of several towns and are locked in combat with the Ukrainian army.
"Russia is continuing to destabilize Ukraine in other ways. Russian irregular forces, Russian-backed forces, and Russian financing are very active in eastern Ukraine. This has to stop," Breedlove told reporters on the sidelines of a meeting of NATO defence ministers in Brussels.
"I think what you see in the east part of Ukraine are very well-led, very well-financed, very well-organised clashes with Ukrainian forces ... seizing Ukrainian buildings ... It is very clear that the Russian influence is a part of this," he said.
Moscow denies such involvement in eastern Ukraine.
US Secretary of State John Kerry has raised concerns with Moscow about reports of Chechens and other fighters crossing into Ukraine from Russia to join the rebellions against the leadership in Kiev.
The Kremlin-backed leader of Chechnya has denied sending fighters to support pro-Russian separatists in Ukraine, but said some could have gone of their own accord.
NATO has made clear it has no plans to get involved militarily in Ukraine but it has sent fighter aircraft and ships to eastern Europe to reassure NATO allies alarmed by Russia's annexation of Ukraine's Crimea region.
Breedlove said all steps being taken by NATO to reinforce its members in eastern Europe would comply with NATO's 1997 agreement with Russia, but he accused Moscow of breaking the pact "when they crossed a sovereign boundary and annexed under fire a portion of a sovereign nation".
He also said that NATO and its member countries were considering a wide range of requests for help from Ukraine, including lethal aid.
Breedlove said Ukraine had put forward a list of items it needed for its military both to NATO and to individual allies and said this included weaponry as well as non-lethal aid.
"They have asked for everything from command and control, communications, help with cyber, help with kinetic capabilities (weapons), help with training, to developing their national guard forces," he said.
Asked if NATO had a position on providing lethal aid, Breedlove said: "That is being discussed and it is inappropriate to remark at this time."
NATO officials say the alliance does not have weaponry to supply. Any decision to supply armaments to Ukraine would be a decision for individual NATO allies.