Alliance chief Jens Stoltenberg said Kosovo's plan was "ill-timed", went against the advice of many NATO countries and would have "serious repercussions".

Kosovo has relied on NATO-led forces to ensure security since the end of the 1998-99 war that effectively cleaved it from Serbia.

Belgrade still refuses to recognise Kosovo's independence and the plans for a military force have caused outrage in Serbia.

"NATO supports Kosovo's security force in its current mandate," Stoltenberg told reporters in Brussels.

"Should the mandate for the Kosovo security force evolve, the North Atlantic Council would have to re-examine the level of NATO's engagement in Kosovo," he said, adding that NATO had made this clear to Pristina on several occasions.

In the latest fiery salvo between the two neighbours, Serbia's Prime Minister Ana Brnabic said Wednesday she hoped Belgrade would not have to resort to military action in response to Kosovo's moves, but warned "it is one of the options on the table".

On Tuesday, Serbian President Aleksander Vucic accused Kosovo of trying to "drive out" the territory's remaining Serb minority with the army plan and by refusing to lift a 100 percent tariff on Serbian goods.

Kosovo says the tariff will remain in place until Serbia recognises its independence.

Stoltenberg urged the two sides to "refrain from provocative steps and statements" and to try to find a compromise.