US Vice President Joe Biden kicks off a short visit to Serbia and its former province of Kosovo on Tuesday.
The veteran lawmaker was a leading advocate of international intervention to stop the Balkan wars in the 1990s and is expected to address regional tensions during his trip.
The agenda was not disclosed, but on his first stop in Belgrade, Biden is expected to discuss Serbia's close relations with Moscow.
An EU membership candidate, Serbia traditionally looks to its ally Russia for support and has refused to join Western sanctions against Moscow over the Ukrainian crisis.
Biden may also raise the unresolved murder of three US citizens in the aftermath of the 1999 war in Kosovo, and the 2008 torching of the US embassy.
The murdered brothers were last seen alive in the custody of Serbian police. Their remains were found in 2001 in a mass grave with bodies of ethnic Albanians killed in Kosovo and buried in eastern Serbia.
The US embassy was set ablaze during riots in Belgrade following Kosovo's declaration of independence from Serbia in February 2008, a move endorsed by the US and Western powers.
Biden is expected to press for a stronger campaign against corruption in Kosovo, a staunch ally of the US since it pushed NATO into intervening against Serbia to end the 1999 war.
A street in Pristina will be named after his deceased son, recognizing Biden's support for Kosovo's fight for independence from Serbia.
In both capitals he is set to push for a faster implementation of EU-brokered agreements aiming at restoring normal diplomatic ties between Kosovo and Serbia.
Serbia has not officially recognized Kosovo as an independent state.
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US Vice President Joe Biden apologised in Belgrade on Tuesday to the families of those killed in NATO's four-month air strikes against Serbia and Yugoslavia in 1999, saying peace and stability in the Western Balkans now were very important for all of Europe, and praising Serbia's leadership in the region, notably in the relations with Croatia.
US Vice President Joe Biden discussed problems from the Balkan's recent troubled past Tuesday in Belgrade, kicking off a short visit to Serbia and its former province of Kosovo.