NATO Secretary-General Jaap de Hoop Scheffer told Serbia and Bosnia on Monday he wanted results in bringing top war crimes suspects Radovan Karadzic and Ratko Mladic to justice by the end of the year.
The arrest of Karadzic and Mladic, both wanted by a UN tribunal for genocide and other crimes during the 1992-95 Bosnian war, has long been seen as crucial to the two Balkan states' hopes of cementing partnership accords with NATO.
De Hoop Scheffer's rare call for results within a clear timeframe comes amid rising frustration in the alliance that the two are still on the run more than 10 years after the war's end.
"I sincerely hope 2006 is the year that Serbia Montenegro and Bosnia Herzegovina meet the criteria for PfP (Partnership for Peace). It is long overdue," de Hoop Scheffer told a New Year's media reception.
"They know what the conditions are," he added. A NATO source said de Hoop Scheffer was referring to progress in bringing Karadzic and Mladic before the Hague-based UN war crimes tribunal, long identified as key to strengthening the two countries' ties with NATO.
A PfP is initially aimed at reinforcing defence cooperation between NATO and non-member countries. Ten of the 30 countries that have signed such accords since 1994 have become members.
Karadzic, 60, political leader in Bosnia during the war, and Mladic, 63, the wartime Bosnian Serb commander, were indicted for genocide charges for the 43-month siege of Sarajevo in which around 12,000 people were killed, and for the 1995 Srebrenica massacre that cost 8,000 lives.
Karadzic is believed to be hiding in the Serb-controlled area of Bosnia, and Mladic in neighbouring Serbia.
UN war crimes prosecutor Carla del Ponte told the UN Security Council last month that Belgrade's cooperation with the court had deteriorated in recent months, and said Bosnian officials must also be held to account for the lack of progress.
Serbia admitted last week that Mladic drew his general's pension up until November while on the run from justice.
NATO is holding several ministerial meetings and one summit of government leaders in 2006, each event a possible platform to extend a formal partnership offer to aspirant countries. NATO envoys in Brussels could also make such an offer at any time.
The European Union opened preliminary talks on membership with Serbia and Montenegro last October but warned that it could suspend them at any time if there was lack of cooperation on war crimes fugitives.