The European Union's foreign-policy chief was met with booing and pro-Russia chants in the Serbian parliament when she called for integrating the Western Balkans into the European bloc.
Far-right Serbian lawmakers, who oppose Serbia's bid to joint the EU and favor closer ties with Russia, banged on benches and chanted "Serbia, Russia, we don't need the union!" during Federica Mogherini's 25-minute address on March 3.
Some lawmakers held banners saying, "Serbia doesn't trust Brussels."
"It's not nice to be rude to a lady," Mogherini said after the speech, but added: "It's a matter of politics.... It's about a difficult political environment here and in the region, and it is also about different ways of interpreting the path that Serbia has taken."
Serbia is deeply split between those seeking integration with the West and those wanting a close alliance with Russia, a traditional Slavic ally.
Mogherini told lawmakers that Serbia played an important role in maintaining peace in the Balkan region.
She said that the EU, Serbia, and the Western Balkans were closely joined and needed each other. Their interconnection is particularly important at this "delicate" moment of tensions in both the region and Europe as a whole, she noted.
"You have a great responsibility," Mogherini said. "Serbia has always been on the crossroads of different worlds."
Tensions have recently mounted in relations between Serbia and its former war foes Bosnia-Herzegovina and Croatia.
Serbia has also refused to recognize the independence of its former province of Kosovo, a key condition the EU has laid down before it will accept Serbia into the bloc.
Political instability also is threatening southern neighbors Macedonia and Montenegro.
"Peace in the Balkans is peace in Europe," Mogherini said at a joint press conference with Aleksandar Vucic, Serbia's prime minister. "We have faced in the recent times -- and we might face in the times to come -- some attempts to put this into question."
Vucic criticized the booing during Mogherini's speech as "not gentleman-like," and insisted that Serbia "remains firmly on the European path."
Mogherini is on a tour of the Balkans that started in Montenegro and will end in Kosovo, trying to reassure the region that the EU remains open for enlargement despite Britain's decision last year to leave the bloc.
Vojislav Seselj, the leader of the far-right Serbian Radical Party, said the chants sent "a clear message that Serbia doesn't want to enter the EU, but wants integration with Russia."
Russia recently declared the Western Balkans to be part of its "sphere of influence," and has taken advantage of growing nationalist sentiment and ethnic frictions in the region to reassert its influence there.