Kosovo, a former Serbian province that declared independence in 2008, is expected to vote next Friday on whether to transform its lightly-armed emergency force, Kosovo Security Force (KSF), into a national army.

Since the end of the 1998-99 war that effectively cleaved it from Serbia, Kosovo has been defended by international NATO-led troops.

On Thursday NATO chief Jens Stoltenberg stressed that Kosovo's army plans are "ill-timed" and go "against the advice of many NATO allies."

But Washington is fully behind the move, US ambassador Philip Kosnett told state broadcaster RTK in Pristina.

"We think that KSF's evolution into Kosovo's armed forces is a positive step and that it is only natural for Kosovo as a sovereign and independent country to have its own defence capability," he said, adding that the US has invested money and training in the emergency force's development.

"This is a process that will take many years," he added.

Belgrade has led the charge in raising concern over Kosovo's army plans, which it has cast as a threat to the 120,000 Serbs still living in the former southern province.

Serbia refuses to recognise Kosovo's independence and still considers it a renegade territory.

Speaking about Pristina's army plans Wednesday, Serbian Prime Minister Ana Brnabic said: "I hope that we will never have to use our army, but at this moment it is one of the options on the table".

More than 13,000 people, mostly ethnic Albanians, were killed in the 1998-1999 war between ethnic Albanian guerillas in Kosovo and Serbian forces.

The conflict ended when a NATO bombing forced Serb troops to withdraw.