(Adds Negroponte)

By Alaa Shahine

KHARTOUM, April 23 (Reuters) - Several international aid agencies said on Monday they were suspending their work in the town of Um Dukhun in Sudan's troubled Darfur region because of attacks on them.

The agencies, which include the British group Oxfam, Save the Children Spain and the U.S.-based Mercy Corps, said the decision would disrupt services to some 100,000 people in the area near the border with Chad and Central African Republic.

The United Nations says about 200,000 people have been killed in the vast western region of Darfur since 2003 when rebels took up arms against the Khartoum government, charging it with neglect. Sudan says only 9,000 people have perished.

A senior U.N. official told Reuters the threat of sanctions against Sudan could help secure a political breakthrough to end a crisis which has left 2.5 million people displaced.

U.S. President George W. Bush warned Sudan's president Omar Hassan al-Bashir last week he had one last chance to stop violence in Darfur or the United States would impose sanctions and consider other punitive options.

Deputy Secretary of State John Negroponte accused Sudan's government on Monday of a campaign of intimidation against aid workers and said time was running out to accept a hybrid force in Darfur or face new sanctions.

"The denial of visas, the harassment of aid workers and other measures have created the impression that the government of Sudan is engaged in a deliberate campaign of intimidation," he said. "Time is running out," Negroponte told reporters.

Britain has also stepped up the threat of sanctions.

"I would hope that the awareness of the sanctions would play a role," the U.N. Secretary General's Special Envoy for Sudan Jan Eliasson told Reuters in an interview in Luxembourg.

"I hope we'll not have to reach that stage, but it's a reminder of realities, of which I hope the parties to the conflict are aware," said Eliasson, trying to work towards a peace accord with the African Union's Salim Ahmed Salim.

ATTACKS ON AID AGENCIES

Aid agencies said attacks on their operations had increased in the past three weeks. In one incident, a humanitarian convoy was shot at and robbed while travelling outside the town in western Darfur, the groups said in a statement.

An aid agency security guard was badly beaten up in another attack and is in a critical condition.

"We greatly regret any suspension, even temporarily, of assistance to people in need," Oxfam and Save the Children Spain said in a joint statement. "But such attacks on humanitarian workers are not acceptable and cannot be tolerated."

The statement said a small number of aid workers would remain to monitor the situation and maintain essential services.

Aid agencies working in the town and in surrounding rural areas help displaced Darfuris as well as refugees fleeing the violence in Chad and Central African Republic.

Rights groups and opposition figures say violence has persisted despite a 2006 peace deal between the government and one rebel faction, threatening the world's biggest humanitarian operation. Khartoum says security in the region is improving.

One rebel group said on Monday that government aircraft bombed the village of Amray in northern Darfur late on Sunday, killing at least two civilians. It said another village in the same area was bombed on Saturday, killing two women.

"Helicopters and Antonov aircraft bombed Amray and killed one woman and a child," rebel commander Jar el-Neby said.

An army spokesman said he was not aware of the attacks. Presidential adviser Majzoub al-Khalifa said government forces had not engaged with the rebels over the past two months.

He called on the rebels to join the peace agreement.

"The door is open for those who did not sign to catch up ... but they cannot stop the peace," he told reporters at a ceremony marking the establishment of the Darfur Transitional Regional Authority, a body charged with reconstruction in the region. (Additional reporting by Ingrid Melander in Luxembourg)

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