U.N. chief prosecutor Carla del Ponte wants to keep up the pressure on Serbia to arrest war crimes suspects, despite NATO's offering of closer ties, her spokesman said on Wednesday (December 6). Another spokesman for the International Criminal Tribunal for the former Yugoslavia (ICTY) commented that the health of hunger-striking Serbian Ultranationalist leader Vojislav Seselj' was of great concern, but it was self-inflicted. Seselj surrendered to The Hague tribunal in 2003 to answer charges of war crimes against non-Serbs in the 1990s and plotting crimes with ex-Yugoslav president Slobodan Milosevic, who died in March months before his trial was expected to end. He has been on a 26 day hunger strike. Serbian war crime tribunal negotiator Rasim Ljajic said on Tuesday (December 5) the country's "action plan" to catch suspected war criminal Ratko Mladic would still go ahead despite Seselj's case. At a news conference on Wednesdy, Del Ponte's spokesman Anton Nikiforov said that the tribunals work progressed, but that it was vital to prosecute the war fugitives, Ratko Mladic and Radovan Karadzic to conclude the work of the tribunal. "But fugitives are key to the completion strategy of tribunal in general. Not only for our work as OTP, but for the tribunal in general to finish our work without Karadzic, Mladic and others, we believe its absolutely unacceptable," Nikiforov said. In May the European Commission froze EU negotiations with Belgrade after Serbia failed to keep a promise to arrest Mladic. But last week NATO decided to invite Serbia, Bosnia and Montenegro to take the first step towards eventual membership of the defence alliance. The ICTY is expected to complete all trials by 2010, and Del Ponte is expected to tell the U.N. Security Council on December 15 that the U.N. tribunal cannot close without trying top fugitives former Bosnian Serb leader Karadzic and his army commander Mladic. Currently the ICTY has been disrupted by Seselj whos health is failing due to his hunger strike. On Tuesday (December 5) a group of Serbian, French and Russian doctors examined Seselj, who has been refusing food and medication, but drinking water. Serbia also asked the U.N. war crimes tribunal to transfer Seselj, to a hospital in Belgrade for treatment. ICTY spokesman, Refik Hodzic said on Wednesday it was Seselj's own decision to risk his health. "(The) tribunal is taking very seriously the situation and in particular the health of Mr. Seselj and you can see that while most of the people are talking about his death, the tribunal keep talking about his life and his health," Hodzic said. Hodzic also said that the tribunal had considered Seselj's demands. "Many of his original requests have already been addressed, including the visitation of his wife and family, including the translation issues, including the issue of his legal adviser, and the only way for him to address the issue of self representation is through the courtroom, through him taking part in the court process. And I will again draw your attention to the fact that when he started refusing food he was representing himself. But also, I would like to emphasize that while tribunal is doing everything in its power to provide Mr. Seselj with medical care and to ensure that he is under the condition which will enable a prompt medical intervention should a medical necessity arrive. It is Mr. Seselj's decision to take this action." Hodzic said. In recent court appearances Seselj pleaded not guilty and routinely disrupted pre-trial proceedings, insulting judges and calling his assigned lawyers "spies" and "actors posing as lawyers". "It is Mr. Seselj who actually holds the key to the decision regarding his health and is not the tribunal. The tribunals position is that we would love to see resolution of this issue by having Mr. Seselj start taking food and medicine again, engage in the court process again, address all his requests within the framework and the rules of the tribunal," Hodzic said. Seselj says he is determined to take his defiance to the bitter end by starving himself to death in detention. The U.N. court ordered Dutch authorities on Wednesday to intervene if necessary -- including possible drip-feeding -- to thwart Seselj's dramatic gesture, but the Radical Party leader has said he will fight any attempt to interfere.