US Vice President Joe Biden called Tuesday for improved ties between former foes Kosovo and Serbia during a visit to the Balkans to promote reconciliation in the fragile region.
Biden held talks with top officials including Prime Minister Aleksandar Vucic in Belgrade, where a group of ultranationalists protested against his visit in T-shirts bearing pictures of US presidential candidate Donald Trump.
Biden said he and Vucic discussed "the importance of moving forward" with ongoing European Union-brokered talks to normalise relations between Serbia and Kosovo, which were at war in the late 1990s.
"It is difficult, there is nothing easy about it, there is a lot of history to overcome," said Biden.
"It's going to take a lot of hard work and political will to overcome divisions."
Kosovo unilaterally declared independence from Serbia in 2008, a move promptly recognised by Washington but consistently denied by Belgrade.
Biden nevertheless praised Serbian efforts towards improved relations.
"If both sides remain committed to the future of peace and greater prosperity it's going to help both nations move closer to joining the European Union," he told reporters.
Biden was due to fly to Kosovo's capital Pristina later Tuesday for the second leg of his trip, expected to be his last to the Balkans as vice president, and he said he would raise the same issue with leaders there.
The Kosovo war, which pitted Serbia's armed forces against separatist ethnic Albanian rebels in the southern province, came to an end after a US-led NATO bombing campaign against Serbia.
During Biden's visit to Belgrade dozens of ultranationalists briefly protested in the city centre, led by Radical Party head Vojislav Seselj who was acquitted of war crimes in late March.
Seselj criticised Biden for encouraging the 1990s NATO bombing and said Trump on the other hand was a "friend of the Serbian people".
Earlier this week Biden hit the 2016 campaign trail with Hillary Clinton for the first time, trashing Trump as unqualified for the White House and accusing him of endangering the lives of US troops.
