European Union accession talks with Serbia and Croatia should be stopped until they hand over key war crimes suspects, a top UN prosecutor has said.
Carla del Ponte said it was "shameful" that major suspects like Bosnian Serbs Radovan Karadzic and Gen Ratko Mladic had not been caught.
The UN's chief prosecutor at The Hague accused Serbia and Croatia of not fully co-operating with the tribunal.
Croatia has responded by promising to give proof of its commitment.
Mr Karadzic and Gen Mladic are accused of war crimes against Bosnian Muslims in the same year.
"The European Union and the United States must stand firm," said Ms del Ponte in a speech in Switzerland.
"Croatia and Serbia and Montenegro... have been co-operating with the tribunal only thanks to the international pressure. Their co-operation is not perfect, nor full."
She said that Mr Karadzic and Gen Mladic must be brought to The Hague this year along with Croatian Gen Ante Gotovina.
EU foreign ministers are discussing Croatia's membership bid at an informal meeting in Wales.
Prime Minister Ivo Sanander said Croatia's request for Greece to extradite a Croatian businessman suspected of helping Gen Gotovina was proof of its willingness to help.
Hrvoje Petrac, 50, was detained on Wednesday in north-western Greece on a boat heading for Italy.
He was sentenced in absentia to six years in jail for kidnapping a boy.
Croatia suspects Petrac of being a key protector of Gen Gotovina.
"Croatia fully co-operates with the tribunal and we will prove it," said Mr Sanander.
Gen Gotovina has been indicted over the murder of Serb civilians during an operation to expel Serb forces from the Krajina region of Croatia in 1995.