A chorus of warnings about Russian meddling in Bosnia

Borrell said a recent decision to beef up the peacekeeper force called EUFOR in Bosnia from 600 to 1,100 personnel had shown the EU's commitment to "unity, to the territorial integrity and sovereignty of Bosnia and Herzegovina."

Borrell pledged to "continue deterring those who would feel emboldened to undertake destabilisation actions."

Bosnia, like Ukraine, has long said it wants to join Nato and the EU.

That's irked Moscow, which wants to maintain control over former Soviet satellites and bulk up its influence in the Balkans in efforts to redraw the post-war security architecture in Europe.

Much of the concern focuses on Bosnian Serbs and their pro-Russian leader Milorad Dodik. They have been challenging state institutions as part of a longtime bid to secede, and that has led the country into its worst political crisis since the end of the Balkan wars of the 1990s.

Dodik was in the European Parliament on Tuesday, along with the other Bosnian leaders, where he insisted he was not seeking to reignite conflict.

Dodik denied he was "under Russian influence" and said he supported the integrity and sovereignty of Ukraine. He said there were "no plans" to secede.

Even so, Dodik called Bosnia "incomplete, unfinished, and impossible" and he blamed "Muslim nationalism" for instability in Bosnia.

Bosnia is made up of two highly autonomous regions, the Serb-dominated Serb Republic, led by Dodik, and a Federation shared by Catholic Croats and Muslim Bosniaks. The two rivalrous regions are linked together by a weak central government, consisting of the three-person presidency, parliament and cabinet.

Šefik Džaferović, Bosniak member of the presidency, also speaking on Tuesday at the parliament, accused Dodik of wanting to break up the country and undermining the Dayton agreement that ended the war in 1995.

Džaferović said Dodik also was fear-mongering to achieve his political goals.

Also in the European Parliament on Tuesday was Željko Komšić, the Croat member of the presidency, who warned that Russia has a long-standing policy of keeping Bosnia locked in a frozen conflict.

"This has to be understood as a security challenge," Komšić told European lawmakers. Keeping ethnic tensions alive, blocking institutions from working, and crony politics were part of Moscow's strategy, he said.

"Russia realised that a frozen conflict represents a security risk for Nato and the EU, and Russia is the biggest advocate for keeping things as they are," said Komšić, in an apparent reference to the way Russia-supporting Bosnian Serbs are keeping the threat of secession alive.

Bosnian Croats also want to see the electoral law amended to bolster their representation, and they have threatened to boycott the general election in October unless the current rules are changed.