KHARTOUM, Sudan - The Sudanese military said it bombed three towns in West Darfur while striking at rebel forces Friday as senior U.N. officials warned that security was deteriorating dramatically in Sudan's vast western region.

The U.N. officials told the Security Council that intensified fighting has worsened the plight of civilians and is hurting chances for a political settlement in the five-year conflict.

Darfur rebels denied any of their fighters were in the towns attacked by the government and said some 200 people were killed. They said helicopter gunships and fixed-wing aircraft battered Sirba, Sileia and Abu Suruj, setting buildings on fire and causing thousands to flee.

"The government attacked using aircraft bombardment, troops and janjaweed (Arab militiamen)," said Abdelaziz Ushar, a senior commander with the rebel Justice and Equality Movement.

Sudan's Arab-dominated government has been accused of unleashing janjaweed forces to commit atrocities against Darfur's ethnic African communities in the fight with rebel groups. At least 200,000 people have been killed and 2.2 million displaced since the fighting began five years ago.

The Sudanese army said its attacks forced rebels to retreat into neighboring Chad, a provocative accusation at a time of escalating tension between the two countries. Both nations accuse each other of hosting hostile rebel groups, allegations that became even more sensitive after Chadian rebels attacked Chad's capital last weekend.

Sudan's "armed forces were able to repulse rebels from the Darfur rebel movements who have retreated into Chadian territories, leaving behind a huge number of dead, wounded and equipment that is currently being counted," the army spokesman, Brig. Osman Mohamed al-Aghbash, said in a statement carried by the country's official news agency.

The commander of a joint African Union-United Nations peacekeeping force that has begun deploying in Darfur to try to stem violence called on the government to halt attacks.

"In addition to the loss of life and damage to property, there is the potential for displacement of large numbers of villagers, compounding an already critical humanitarian situation," said Gen. Martin Agwai. "It is important that all sides show full restraint at this time, and that space be allowed for immediate mediation."

In New York, U.N. peacekeeping chief Jean-Marie Guehenno and the top U.N. political mediator in Darfur, Jan Eliasson, painted a grim picture of a worsening conflict a year after the U.N. and African Union launched a new effort to get a political settlement.

Guehenno said the "very disturbing new spike in violence" Friday followed December attacks on Sudanese troops in the same areas by rebels from the Justice and Equality Movement who are trying to consolidate their positions north of El Geneina.

"So what we are witnessing is actually a war with offensive, counteroffensive fighting," Guehenno told the Security Council.

Eliasson urged the Sudanese government and all rebel groups to "unilaterally declare and respect a cessation of hostilities." He urged the Security Council and countries with influence with the two sides to send a message that the fighting must stop.

"Over the last few months, the security and humanitarian situation in Darfur and the region has dramatically deteriorated, most recently through events related to Chad," he said.

This has hampered efforts to finalize preparations for substantive talks between the government and rebel groups or to initiate confidence-building measures, Eliasson said.

The deployment of just 9,000 of the expected 26,000 troops and police in the AU-U.N. force and the continued tensions between Chad and Sudan have also had "detrimental consequences for the Darfur political process," he said.

Key rebel leaders boycotted peace talks convened in Sirte, Libya, in October, but Eliasson and his African Union counterpart, Salim Ahmed Salim, have been working intensely with the various factions to get agreement on a new session.

More than a dozen rebel movements have now coalesced into five groupings, but there are still unresolved leadership issues and the rebels still have to prepare for negotiations, Eliasson said.

"Thus, prospects for quick agreements on common positions and a negotiation team appear dim," he said.

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