KIEV, Ukraine (AP) — NATO’s chief defied mounting Russian belligerence Thursday with a pledge to provide assistance to Ukraine, which is battling to quash an insurgency being waged by pro-Russia rebels in the country’s east.

The show of support from Anders Fogh Rasmussen comes as government troops increasingly focus their push to claw back rebel-held territory on the stronghold of Donetsk. Ukraine appears to be ratcheting up the urgency of its onslaught against the backdrop of an alleged escalation of Russian troop presence on the border.