China expressed "grave concern" yesterday after the International Criminal Court's prosecutor charged Sudan's President with genocide in Darfur.

In Khartoum, the UN told its staff to stay at home as thousands of Sudanese prepared to rally in support of President Omar Hassan al-Bashir.

ICC Prosecutor Luis Moreno-Ocampo on Monday asked the court for an arrest warrant for Mr Bashir, accusing him of running a campaign of genocide that has killed 35,000 people and forced 2.5 million to flee their homes in Sudan's western region.

Sudan viewed the ICC's move as "irresponsible, illegal and unprofessional", according to Vice President Ali Osman Mohamed Taha.

At a regular news conference in Beijing, Chinese Foreign Ministry spokesman Liu Jianchao said: "China expresses grave concern and misgivings about the International Criminal Court prosecutor's indictment of the Sudanese leader".

"The ICC's actions must be beneficial to the stability of the Darfur region and the appropriate settlement of the issue, not the contrary," Mr Liu said.

China, Khartoum's biggest arms supplier and a major investor in its oil industry, now faces difficult choices over its relationship with Mr Bashir just as the Beijing Olympics opens a soft spot for international pressure.

Beijing has sought to balance its energy and political interests in Sudan with its desire for a respected seat at the table in Darfur peace efforts.

Asked whether China would support a UN resolution suspending the ICC's actions against Mr Bashir, Mr Liu avoided firm answers.

"China will continue consultation with other members of the United Nations Security Council, but as for the outcome, that I don't know," he said. Mr Liu confirmed that 172 Chinese engineers would head to Darfur today, bringing all of its 315 promised peacekeepers into place.