A US pilot and the Serb officer who downed his plane during a 1999 NATO air war barely hid their tears as they reunited in Belgrade Monday, on the eve of US Secretary of State Hillary Clinton's visit to Serbia.

Dale Zelko, a former US Air Force pilot whose F-117 stealth plane was shot down by ex-Serbian army officer Zoltan Dani on March 27, 1999, attended the Belgrade opening of the documentary "Second Meeting", a 90-minute story on how the former foes became close friends.

"I am sorry for your suffering and sorrow, loss and anguish.... I am sorry for the war," said Zelko in a trembling voice after the screening.

Tearful and visibly shaken, Zelko said he was "so grateful and thankful... to be on this journey with the Dani family."

Dani, also visibly touched, said the film should be seen as "a message of peace".

"War is not between normal, average people, it is between the governments.... The politicians are the ones who decide this," Zelko said, greeted by a standing ovation in the packed Serbian cinema.

Zelko said he was aware that Clinton was coming to Belgrade Tuesday and told AFP his message would be: "Let's not ever do this war again, let's do everything possible to work out any sort of problems or differences with mutual respect and admiration for each other."

The shooting down of the F-117 in Budjanovci, near Belgrade, by Dani's anti-aircraft missile battery was one of the most surprising military achievements by the poorly equipped Serbian army during the 78-day NATO bombing campaign launched to end the regime's repression of independence-seeking Kosovo.

It was the only time an F-117, touted as invisible to radar, was ever lost in combat.

Zelko was rescued by a NATO helicopter and transferred back to the alliance base in Italy before returning to the United States.

"That mission was my last combat. I have never flown (the plane) again," Zelko said.

Dani, who had also left the military and opened a bakery, said he met Zelko through the documentary's director Zeljko Mirkovic.

"Zeljko asked me what I would tell to the man I had shot down. I answered that I would invite him for a drink as he was also just doing his job," Dani said earlier.

The two men's families have become friends and meet regularly, and close bonds have formed between their children.

"The war was not between him and me, it was not a personal thing, or between me and the Serbian people," said Zelko.

"War is a terrible thing. It would be amazing and wonderful if we never had to do it," he said.

The documentary was also screened in New York and Washington. It will tour Serbia in the coming days.

Clinton, who arrived Monday in Bosnia to kick off a five-nation tour of the Balkans, was due to arrive in Belgrade on Tuesday, before heading to Kosovo.

Together with EU foreign policy chief Catherine Ashton, Clinton will "reiterate US-EU resolve for Serbia and Kosovo to build on previous agreements and advance their dialogue, as well as to encourage concrete steps that will allow those countries to progress on their respective paths to EU membership," the State Department said.

Thirteen years after the end of NATO's bombings, Serbia still rejects Kosovo's unilateral 2008 proclamation of independence, which is recognised by some 90 states, including 22 of the EU's 27 members and the United States.