"Welcome home," Kosovo President Hashim Thaci told Clinton, who is beloved there for sending US jets to join the 1999 air strikes against the regime of former Serbian strongman Slobodan Milosevic.

June 12, 1999, the day when NATO entered Kosovo after its three-month assault on Serb forces, marks the moment Belgrade effectively lost control of its former province.

It was the end of a brutal conflict between Serbian forces and ethnic Albanian rebels that had claimed 13,000 lives, mostly Kosovo Albanians, in the final war of Yugoslavia's collapse.

"I love this country, and it will always be one of the great honours of my life to have stood with you against ethnic cleansing and for freedom," Clinton told hundreds gathered in the centre of Pristina -- where he already has a statue and boulevard in his name.

While saying that Kosovo still had some way to go in terms of building a "truly inclusive nation," he added: "Relax, no one has solved that yet."

On the 20-year anniversary, Kosovo leaders have been toasting to its liberation, with tributes on social media this week signed with the hashtag #Kosovo20YearsFree.

Adnan Shuki, a 67-year-old who joined the crowd in Pristina waving Kosovo and US flags, recalled June 12 as "the happiest day in the history of Kosovo Albanians".

"We'd been away from home, bombed, mistreated, wasting years without work," he said.

Yet Kosovo's path to statehood since then has been anything but smooth.

Belgrade still refuses to officially accept the independence its former province declared in 2008, undercutting Kosovo's efforts to gain global recognition.

While Kosovo has the backing of the US and most of the West, Russia and China also reject its statehood, effectively shutting it out of the UN.

There is widespread disillusionment with corruption and economic problems that have festered over the past two decades.

"Kosovo remains a weak state, with minimum justice and with maximum unemployment," opposition politician Albin Kurti wrote on Facebook.

"Twenty years is a long time for people under the domination of a dozen tycoons."

- 'Move forward' -

Wednesday's ceremonies will also see the unveiling of a new bust of Madeleine Albright, who was US Secretary of State at the time and spoke during the ceremony.

But there was no celebration in northern Kosovo, a region dominated by ethnic Serbs who remain loyal to Belgrade.

"They celebrate their friends, they do it because they have nothing of their own. A statue for Madeleine Albright, Clinton has one already -- for me, it's pathetic," said Dragoslav Jovic, a 69-year-old in the city of Mitrovica.

The NATO intervention remains a raw memory for many in Serbia, with some buildings in Belgrade still bearing the damage.

Earlier in the week, Serbian President Aleksandar Vucic slammed the 1999 intervention as "the 19 most powerful countries attacking a small country committed to freedom."

"They have caused us enormous damage from which we are still recovering," he added.

The NATO strikes battered Serbian military targets and infrastructure for 78 days, also killing an estimated 500 civilians, including Serbians, Albanians and Roma, according to Human Rights Watch.

The anniversary comes at a time when already dismal relations between Kosovo and Serbia have tumbled to a low point in recent months.

A series of diplomatic clashes have soured long-running talks aimed at reaching an accord.

Speaking after Clinton in Pristina, US Deputy Assistant Secretary of State Matthew Palmer urged Kosovo to bolster efforts to secure a deal with Serbia.

"The status quo in the Balkans is not sustainable. If Kosovo is not moving forward, it will drift backward," he said.

"There is no better time than now."

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