MONS, Belgium, Aug 28 (Reuters) - NATO believes well over 1,000 Russian troops are operating inside Ukraine, a NATO military officer said on Thursday.
The officer, briefing reporters on condition of anonymity, referred to the Russian actions as "incursions" rather than an invasion.
"We assess well over 1,000 Russian troops are now operating inside Ukraine," he said at NATO's military headquarters in southern Belgium. "They are supporting separatists (and) fighting with them."
Ukraine accused Russia on Thursday of bringing troops into the southeast of the country in support of pro-Moscow separatist rebels.
The NATO officer showed reporters a satellite picture, dated Aug. 23, of Russian self-propelled artillery lined up inside eastern Ukraine.
"This is highly sophisticated equipment which requires a well-trained crew. It takes months to train crews like that. It's extremely unlikely these sorts of units are manned by separatists," he said.
"Russia is trying to prevent a defeat of the separatists and wants to hold on to this area. The recent upsurge and now even direct involvement of Russian troops inside Ukraine is aimed at this," the official said. (Reporting by Adrian Croft, Editing by Angus MacSwan)