PRISTINA (Reuters) - Kosovo signaled on Wednesday it would turn its security force into a national army, in plans opposed by its ethnic Serb minority that drew immediate criticism from NATO and the territory’s biggest foreign supporter, the United States.

Members of Kosovo Security Forces (KSF) march during a celebration marking the eighth anniversary of Kosovo's declaration of independence from Serbia, in Pristina February 17, 2016. REUTERS/Marko Djurica

Nearly two decades after the Kosovo war, relations between Belgrade and Pristina remain strained, and Serbia continues to regard Kosovo, which declared independence in 2008, as a renegade province.

The Kosovo government ordered the creation of a national army three years ago, but Serbian deputies said they would block the required changes to the constitution.

On Wednesday parliament indicated it would bypass that opposition by preparing amendments to an existing law that would allow the Kosovo Security Forces (KSF) to buy heavy weapons, effectively turning it into an army.

NATO, which has some 4,500 soldiers stationed in Kosovo, said the plan raised serious concerns.

“I made clear that unilateral steps such as these are unhelpful,” the Atlantic alliance’s Secretary General Jens Stoltenberg said in a statement after talks with the territory’s president and prime minister.

The U.S. embassy in Pristina said adoption of the amendments “would force us to re-evaluate our ... longstanding assistance to Kosovo’s security forces.”

A vote is expected in the coming days. Serb deputies, who number just 11 in the 120-strong chamber but whose support would be needed to change the constitution, said they would boycott the session.

Kosovo President Hashim Thaci, who initiated the creation of the army, said he would continue with his plans despite NATO and U.S. concerns. He called on the government and parliament to approve the law.

“Serbia is against our army... At the same time it fills its air space with MIG planes donated by Russia,” Thaci said at a news conference after meeting U.S. and other western European ambassadors in his office.

“We have been waiting for the will of these (Serb) MPs for three years. We don’t see that coming and we cannot wait for them in eternity, we are forced to move with the law and transform the KSF into an army.”

Thaci said his western allies had told him they were not against a Kosovo army but they wanted to find a joint way to resolve the issue.

Serbia’s Foreign Minister Ivica Dacic said on Monday that the new law would cause “instability in the region.”

It aims to create a new army of 5,000 active soldiers and 3,000 reservists. The KSF, meanwhile, is a lightly armed, 2,500-strong force trained by NATO and tasked with crisis response, civil protection and ordinance disposal.

NATO arrived in Kosovo - a landlocked country of 1.8 million people that borders Serbia, Albania, Montenegro and Macedonia - in June 1999 following weeks of air strikes to halt the killing and expulsion of ethnic Albanian civilians by Serbian forces fighting a two-year counter-insurgency.

NATO has said it has no plans to leave Kosovo for now.