The chief prosecutor at the UN war crimes tribunal in The Hague, Carla Del Ponte, has told the BBC that "all possible measures" should be taken against Serbia over Belgrade's reluctance to arrest those indicted for crimes in the former Yugoslavia.
Ms Del Ponte believes at least 12 of the fugitives from justice are living in Serbia - some of them openly.
Slobodan Milosevic says Ms Del Ponte is "the new Gestapo"
The US has already frozen some aid to Serbia, but Ms Del Ponte called for "even stronger pressure," involving "diplomatic, economic and financial" sanctions.
And she accused Serbian Prime Minister Vojislav Kostunica of "doing nothing" to catch the indictees.
"What I can say is that Kostunica, for political reasons, doesn't want to arrest the fugitives - because he told me that personally in our last meeting," she told BBC World Service's The Interview programme.
Ms Del Ponte has already told the UN Security Council that Serbia is "the single most important obstacle," although she admitted she had "no proof" Serbia was protecting the men.
New EU role
Mr Kostunica is concerned that the apprehension of some of the accused, who are regarded by many Serbs as national heroes, could destabilise his minority government or perhaps Serbia itself.
However the European Union has said it will not negotiate with Serbia over EU membership until the indictees are handed over.
"That is extremely important," Ms Del Ponte said.
"That is the only leverage they can use, and can, I hope, have results."
She also expressed hopes that the EU could bring further pressure to bear in Bosnia-Hercegovina.
Bosnian Serb wartime leaders Radovan Karadzic and General Ratko Mladic - the two most wanted suspects - remain at large.
On Thursday, the EU took over from Nato's S-For operation in Bosnia, embarking on the EU's largest-ever peacekeeping mission.
Ms Del Ponte said she had received "some indication" that with the transfer of power things would change, and that she would be able to get the indictees before 2008 - the deadline for the end of the tribunal.
She accused Nato of not having the political will to get the indictees and bring them to The Hague.
"It isn't acceptable to us, because Nato - who are controlling the territory in Bosnia-Hercegovina - of course have enough intelligence to locate all the fugitives," she said.
"We give information, but the problem is they don't give feedback, so we never know what they have done with our information."
She added that at one point she had complained, and there had been a change in Nato's attitude "some months ago," but that was "too late."
However, Brig-Gen Steven Schook, Nato's outgoing commander in Bosnia, said in November that he was "absolutely not" embarrassed that Radovan Karadzic remained free.
Instead, he said that he was "very proud" of what S-For had accomplished and that the suspects' "support network" in Bosnian Serb areas had made arresting them "more difficult."
Ms Del Ponte also defended her work at the war crimes tribunal, where she has been prosecuting the case against former Yugoslavia President Slobodan Milosevic. He has described her as "the new Gestapo".
Some commentators have suggested that her case has lacked a "smoking gun" and has featured only circumstantial evidence.
But Ms Del Ponte said she believed prosecutors had proved the genocide charge against Mr Milosevic.
Ms Del Ponte is angry more war crimes indictees have not been found
The case has so far run for two years and media interest in it has dropped significantly - something Ms Del Ponte said she was very grateful for.
"We are pleased not to be under examination every day from the press, from the media, from criticism all around," she stated.
"I think it is important that we finish this trial - and have the sentence. So we are working in a much more quiet manner, and it is much better - better for us, and better for international justice."