Kosovo’s president Hashim Thaci said on Friday he would resign and force a parliamentary election if lawmakers do not approve changes that would effectively create a national army under a plan opposed by the country’s ethnic Serb minority and its NATO and U.S. allies.

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 and recruit more soldiers, in effect transforming it into an army.

The plan drew immediate criticism from NATO, which still has some 4,500 troops in the country nearly two decades after it attacked Serbia because of Kosovo. Kosovo unilaterally proclaimed independence in 2008 and is recognized by over 100 UN member states. Serbia, as well as Russia, China, Israel, Iran, Spain, Greece and other countries don’t recognize Kosovo’s independence.

“If MPs will not vote in favor, I will resign as president that second,” President Hashim Thaci, whose former political party is the biggest in parliament, said in an interview on Friday evening with state television channel RTK. “A legislature that will not vote for the army of its own country should go home.”

In an interview with Sputnik Serbia, Milovan Drecun, chairman of the Serbian parliament’s Committee for Kosovo and Metohija, specifically underscored the importance of adhering to a relevant UN resolution on the issue.

“A KFOR mission and NATO should respect UN Security Council Resolution 1244, which does not stipulate creating Kosovo’s army. Meanwhile, relevant preparations have taken place for several years now, with NATO instructors training Kosovo soldiers. Actually, NATO created this army, which is why it’s clear that Thaci [should] avoid making steps that would be out of line with the position of NATO and the most influential members of the alliance,” Drecun said.

He added that “NATO and the US are trying to give a kind of legitimacy to Kosovo’s move [to create its army], because even for them it is unacceptable that the Serbs, the second most influential national community in the province, were excluded from this process.”

Drecun also said that Kosovo Serbs and Belgrade should [be engaged in] more diplomatic efforts within the UN, the EU and NATO in a bid to prevent Thaci from implementing his plans.

“It is necessary to point out to everyone that the [possible] Kosovo national army would become an additional destabilizing factor in the already destabilized situation,” Drecun stressed.

Meanwhile during telephone talks with Serbian Prime Minister Aleksandar Vucic on Wednesday, Thaci warned Belgrade against interfering in the domestic affairs of the “sovereign state”, but said that Vucic should make Serbian MPs support Pristina’s push for creating the Kosovo army.

The row over the army has left Kosovo at odds with its western backers over a big issue for the first time and it remains unclear what prompted Thaci to suddenly shift his policy.

NATO and the United States said on Wednesday they would re-evaluate the assistance they have long provided to the KSF if the changes are approved.

“I made clear that unilateral steps such as these are unhelpful, and I urged the Kosovo authorities to remain in close contact with Serbs in Belgrade,” NATO Secretary General Jens Stoltenberg said.

The U.S. ambassador to Kosovo, Greg Delawie, tweeted late on Friday: “The U.S. believes Kosovo’s security depends on the quality of its partnerships. We don’t want to see Kosovo out of step with key partners.”

NATO, whose troops help maintain the fragile peace, said it would prefer that the new republic changes its constitution to create an army.

That would require the support of the 120-seat parliament’s 11 Serb deputies, who – backed by Belgrade – have said they will never accept the plan to create a force of 5,000 active soldiers and 3,000 reservists.

The KSF is a lightly armed, 2,500-strong force trained by NATO and tasked with crisis response, civil protection and ordinance disposal.

NATO has said it has no plans to leave Kosovo but the dispute with key allies over the army has alarmed some.

“The United States is very important for Kosovo and its people,” Arben Gashi, a lawmaker from Prime Minister Isa Mustafa’s Democratic League of Kosovo (LDK) party said on Friday. “As for Hashim Thaci, he can easily be replaced.”