War crimes prosecutors for the former Yugoslavia say they cannot meet U.N.-imposed deadlines for completing their work. War crimes tribunals are being hampered by heavy caseloads, missing suspects, and a lack of cooperation from states where fugitives are hiding.

Nearly 10 years after Yugoslavia witnessed horrific war crimes, including genocide, chief prosecutor Carla Del Ponte expressed irritation that some of the most notorious fugitives remain at large. Briefing the U.N. Security Council, she said the war crimes tribunal at The Hague cannot complete its mission until at least three key suspects are brought to trial.

"As long as Radovan Karadzic, Ratko Mladic and Ante Gotovina manage to escape justice and defy the international community, the work of this tribunal will remain unfinished," Ms. Del Ponte  says.

Ms. Del Ponte noted a major improvement in the attitude of Serbian authorities in cooperating with her investigation into the 1995 Srebrenica massacre of nearly eight-thousand Muslim men and boys. But she accused the government of Serbian Prime Minister Vojislav Kostunica of not doing enough to hand over key suspects Radovan Karadzic and Ratko Mladic.

"Prime Minister Kostunica gave me assurances that his government will deliver on these remaining fugitives, and I expect him to fulfill his commitment. However, as I understand, he is not willing to carry out arrest operations," Ms. Del Ponte  says.

Ms. Del Ponte says she will refuse to participate in any commemoration of the Srebrenica massacre unless Mr. Karadzic and Mr. Mladic are arrested.

The head of the Yugoslavia tribunal, Judge Theodor Meron, said it is already unlikely the court can finish its work by the 2008 deadline. If high-profile suspects are arrested, that work could run months, even years, longer.

"If no new fugitives arrive, and if no guilty pleas are entered, the tribunal could complete its current caseload sometime in 2009," Mr. Meron says. "But all of those ifs indicate that these estimates are based on assumptions that evolving reality will modify."

Judge Meron said persons accused of war crimes must not be allowed to hide in hopes that the tribunal would close its doors before they are arrested.

Neither Judge Meron nor chief prosecutor Del Ponte made note of information that Ratko Mladic might be negotiating his surrender to the tribunal.

U.S. Undersecretary of State Nicholas Burns told reporters last Friday that Mr. Mladic's capture could be near. That comment came amid press reports that Serbian authorities know where Mr. Mladic is hiding.

The United States had been dissatisfied with the record of the Belgrade government's cooperation on war crimes indictees, and had frozen delivery of reconstruction aid. But Undersecretary Burns announced a resumption of aid last week, saying the attitude of Serb authorities had changed.