BRUSSELS (AFP) - Reports of pro-Russian groups in eastern Ukraine acquiring heavy weapons from Russia, including tanks, would mark a "serious escalation" of the crisis if confirmed, Nato said on Friday.
"We have seen reports that Russian tanks and other armoured vehicles may have crossed the border into eastern Ukraine," Nato head Anders Fogh Rasmussen said.
"If these reports are confirmed, this would mark a serious escalation of the crisis in eastern Ukraine," Mr Rasmussen said in a statement.
The secretary-general repeated Nato calls for Russia to complete the withdrawal of troops it had massed on the Ukraine border and to halt the flow of weapons and fighters into the war-torn eastern part of the country.
The US-led military alliance, along with the European Union, has consistently urged Russia to "de-escalate" the crisis, failing which it faces the prospect of even tougher sanctions than the travel and asset freezes so far imposed on Russian and Ukrainian figures blamed for stoking the conflict.
In the latest fighting in eastern Ukraine, which has so far claimed 270 lives, government forces said they had retaken the strategic rebel-held port of Mariupol.