The announcement late last year that the Kosovo Security Force (KSF), a lightly-armed emergency force, would be transformed into a standing army had US backing but alarmed many European countries.

Stoltenberg said several NATO countries felt the move was "ill-timed" and so the alliance would reassess its work in Kosovo -- though he said the KFOR peacekeeping mission would not be affected.

"What we will assess (are) the activities we have outside the KFOR mission, which is different kinds of capacity-building," Stoltenberg said.

"We have not made any decisions but we have made clear we will assess the level of NATO engagement because several allies have expressed they think it's ill-timed, the decision to transform the KSF into an army."

Kosovo, whose population is mostly ethnic Albanian, broke away from Belgrade after a bloody 1998-99 guerrilla campaign and the NATO bombing of Serbian targets.

Serbia refuses to recognise its independence and EU-led efforts to improve ties have stalled. Kosovo has slapped 100 percent tariffs on Serbian goods and has resisted pressure from Brussels and Washington to drop the measure.