THE HAGUE  - The prosecutor for the International Criminal Court sought Monday the arrest of Sudanese President Omar al-Beshir for alleged war crimes in strife-torn Darfur. Prosecutor Luis Moreno-Ocampo said in a statement that Beshir had "masterminded and implemented" a plan to destroy a large portion of three ethnic groups in Sudan. His appeal to the court's judges marked the first time the arrest of a sitting head of a state had been requested at the ICC. The move came despite fears and warnings that it could enflame tensions in Darfur and lead to the expulsion of aid workers and peacekeepers in Sudan's western region. "ICC Prosecutor Luis Moreno-Ocampo has presented evidence today showing that the Sudanese President committed the crimes of genocide, crimes against humanity and war crimes in Darfur," his office said in a statement. Moreno-Ocampo "has concluded there are reasonable grounds to believe that (Beshir) bears criminal responsibility in relation to 10 counts of genocide, crimes against humanity and war crimes." Judges will now examine the application to ascertain whether reasonable grounds exist to believe that a crime within the court's jurisdiction had been committed, before deciding whether to issue a warrant or not - a process that could take several months. Meanwhile, a Sudanese government spokesman immediately rejected a call from the International Criminal Court prosecutor to arrest President Beshir and threatened further "reaction" if the issue goes to the United Nations. "Now we are against the ICC and we reject any decision from the ICC," government spokesman Kamal Obeid told AFP. Asked if the Sudanese government would make a specific reaction against the United Nations, Obeid replied: "Now we are against the ICC. If the ICC transfers the matter to the UN, then we will have a new reaction." He declined to elaborate. About 1,000 demonstrators rallied in Khartoum Sunday, denouncing the anticipated charges at a government-sponsored protest as Beshir chaired an emergency cabinet meeting. Western embassies have advised nationals to limit unnecessary travel and the United Nations has stepped up its security levels amid fears that the ICC prosecutor's move could spark violent retaliation. Western officials fear Sudan could expel members of the United Nations and African Union peacekeeping mission in Darfur, or aid groups. Contingency plans have been made for an evacuation and non-essential staff have been told to stay at home on Monday. Fears have also been voiced that naming Beshir could embolden Darfur rebels who attacked Khartoum in May. On Tuesday last week, seven UN peacekeepers were killed and 22 were wounded in the ambush of a UN convoy in Darfur that some blamed on state-backed militia. The world body says up to 300,000 people have died since the Darfur conflict broke out in February 2003. The Sudanese government puts the death toll at 10,000. The conflict began when African ethnic minority rebels took up arms against the Arab-dominated regime and state-backed Arab militias, fighting for resources and power.