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The Sudanese government has responded angrily after an international prosecutor accused President Omar al-Bashir of genocide in Darfur.
Sudan's UN envoy said the International Criminal Court had no jurisdiction in Sudan and that it would not co-operate.
And Vice-President Ali Osman Taha said the evidence was false and indicated Sudan may try to halt the court's work.
A pro-government rally is due to take place in Khartoum soon and the UN is to begin removing some staff from Darfur.
The United Nations said the decision to pull back some non-essential staff came after recent violence and as a precaution after the genocide accusation.
Judges at the International Criminal Court (ICC), an independent body, have still to decide if there are reasonable grounds to issue an arrest warrant against Mr Bashir.
Sudan's president is quoted by Reuters as saying the accusations are lies.
'Irresponsible move'
Sudan's ambassador to the UN, Abdalmahmood Abdalhaleem Mohamad, told the BBC that Mr Bashir viewed the charges as a "political statement" and had no intention of co-operating with the ICC.
He criticised ICC prosecutor Luis Moreno-Ocampo for indicting the president, whom he said had brought about a peace agreement to end Sudan's civil war.
"It is a very irresponsible move, it will affect negatively the peace process in the country," he said.
"It will have ramifications in the entire region. Our priority is peace in the country. Stopping bloodshed, making peace."
Mr Mohamed told the Associated Press that the government was bolstering its military capability in case rebel forces were encouraged by the situation to attack Khartoum.
Meanwhile, Sudan's vice-president said that although the authorities would endeavour to protect humanitarian staff working on the ground in Darfur, they could not guarantee their safety.
Speaking on behalf of the African Union chairman, Tanzanian Foreign Minister Bernard Membe urged the ICC to suspend its decision on whether to seek Mr Bashir's arrest until problems in Darfur were resolved.
Sudan's government is expected to meet friends from the Arab League on Saturday, reports the BBC's Karen Allen in Khartoum, to chart the way forward.
It will also seek to defend itself against what many consider to be an assault not only on the country's sovereignty but also an attack on Islam, our correspondent says.
On 8 July, seven peacekeepers of the joint UN-African Union Darfur mission, Unamid, were killed and 22 injured when they were attacked by heavily armed militia in northern Darfur.
As of May this year, Unamid included nearly 9,600 uniformed personnel and about 1,300 civilian staff, both international and local.
It is not clear how many will be withdrawn.
The UN - which has no influence over the ICC - runs large-scale humanitarian operations in the region.
A Sudanese official told the BBC that he had been informed by Unamid the evacuation would begin on Tuesday, and that the Sudanese government had had no say in the decision.
Security Council moves
Sudan's president was accused of genocide, crimes against humanity and war crimes in Darfur by Mr Moreno-Ocampo.
He told judges at The Hague that Mr Bashir bore criminal responsibility for alleged atrocities committed over the past five years.
Sudan has refused to hand over two suspects who Mr Moreno-Ocampo charged last year, Humanitarian Affairs Minister Ahmad Harun and militia leader Ali Kushayb.
The BBC's Laura Trevelyan at the UN in New York says that Mr Ocampo was asked by the Security Council to investigate the killings in Darfur - and this means the 15-member body also has the power to suspend his work on the case for a year.
Behind the scenes, our correspondent says, Sudan has been lobbying China, Russia and African nations on the Security Council to see if it can win the nine votes needed to pass a resolution to do that.
It would be difficult for countries which recognise the ICC to vote to stop the prosecutor's work, as this would seem to undermine the court, she says.
But if there is a widespread feeling at the UN that Mr Ocampo's charges against Mr Bashir are destabilising Sudan, then the mood could change, our correspondent concludes.
Some 300,000 people have died as a result of the conflict in Darfur since 2003 while more than two million people have fled their homes, the UN estimates.
Sudan's government denies mobilising Arab Janjaweed militias to attack black African civilians in Darfur since rebels took up arms in 2003.
PHOTO CAPTION
Sudan's President Omar Hassan al-Bashir salutes during the ceremony of signing Sudan's new election law in Khartoum July 14, 2008. (Reuters)
BBC