U.S. Vice President Joe Biden offered his condolences to the families of those killed in the Balkan wars, including those killed in the NATO airstrikes on Serbia in 1999.
Biden's overtures came on the first day of his trip to Serbia and Kosovo, aimed at encouraging the two Balkan states to mend ties.
"I'd like to express my condolences to the families of those whose lives were lost in the wars of the 1990s, including those killed as a consequence of the NATO airstrikes," Biden told reporters after talks with Serbian Prime Minister Aleksandar Vucic.
As a senator, Biden was a strong advocate of the NATO bombing of Serbia in the 1990s. He once said that his work to end the Yugoslav wars was one of the "proudest moments'' of his long political career.
The U.S.-led bombardment in 1999 stopped Serbia's crackdown against ethnic Albanian separatists, ending Belgrade's rule over its former province of Kosovo.
Serbia does not recognize Kosovo, its former southern province, as sovereign but has struck a series of deals brokered by the European Union to try to regulate relations between the two.
In Belgrade, Biden was greeted by hundreds of Serbian ultra-nationalists chanting "Vote for Trump! Vote for Trump!"
While the United States is highly popular among Kosovars, who regard Washington as their savior, resentment remains high in Belgrade over NATO's airstrikes.
Trump's volatile campaign, which has included calls for a border wall with Mexico to keep out immigrants and a temporary ban on Muslims entering the United States, has piqued the interest of some right-wing and nationalist leaders abroad.
Biden, on his last trip to the Balkans as a senior American official, traveled later Tuesday to Kosovo.