NATO Secretary-General Jens Stoltenberg said he spoke on Thursday with both Serbian and Kosovo leaders about Kosovo’s plan to form a regular army, a move that has been strongly contested by Serbia and the alliance, AP reported.

A statement from Kosovo’s government said Ramush Haradinaj assured Stoltenberg the transition from the Kosovo Security Force into a regular army would be done in close cooperation with NATO.

Serbian President Aleksandar Vucic said in a statement that he expressed concern about Kosovo’s plan because it represents “a danger” for the “survival” of the Serb minority in Kosovo and that it could jeopardize regional stability and peace.

Stoltenberg said in a statement that both Serbian and Kosovo officials should “show calm and restraint, and avoid any provocative statements or actions.”

He said he had warned Haradinaj that NATO would “examine the level of our engagement with the Kosovo Security Force.?”

“I stressed that such a move is ill-timed, goes against the advice of many NATO allies, and can have negative repercussions on Kosovo’s prospects for Euro-Atlantic integration,” Stoltenberg said.