BELGRADE (Reuters) - U.S. Vice President Joe Biden, visiting Belgrade on Tuesday to encourage Serbia and Kosovo to normalize relations, offered condolences to Serbs who lost loved ones in U.S.-led NATO air strikes during the 1999 Kosovo conflict.

Biden was the first high-ranking U.S. official to make such a gesture following NATO's intervention in the Kosovo conflict, which led to the ethnic Albanian-majority region's declaration of independence from Serbia in 2008.

The United States is highly popular among Kosovars, who regard Washington as their savior for the air strikes that halted killings of ethnic Albanians by Serbian forces waging a counter-insurgency war.

But resentment remains high in Belgrade over NATO's air strikes, whose vestiges can be seen in battered ex-Defense Ministry buildings in the center of the Serbian capital.

"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 air strikes," Biden told reporters after talks with Serbian Prime Minister Aleksandar Vucic.

NATO Secretary General Jens Stoltenberg offered similar condolences last year.

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. Analysts and Western diplomats say implementation of the agreements has been piecemeal at best on both sides.

(Reporting by Ivana Sekularac; writing by Ingrid Melander; editing by Mark Heinrich)