(Adds U.S., British and Libyan ambassadors, U.S. State Department)

By Louis Charbonneau

UNITED NATIONS, Jan 9 (Reuters) - Sudan on Wednesday denied U.N. accusations that Sudanese government forces attacked a U.N.-African Union supply convoy in Sudan's Darfur region this week, pointing the finger at Chadian-backed rebels instead.

A spokeswoman for United Nations Secretary-General Ban Ki-moon had said on Tuesday that "elements of the Sudanese armed forces" had attacked the convoy from the joint peacekeeping mission in Darfur, known as UNAMID.

"They were not the government," Ambassador Abdalmahmoud Abdalhaleem told reporters before a meeting of the U.N. Security Council on the situation in Darfur.

"The rebels did that. No doubt about it," he said, referring to an attack in the war-ravaged area of West Darfur late on Monday.

"It happened in an area infested with rebel activities. The Justice and Equality (Movement) elements in West Darfur did that with the massive support ... they enjoy from the Chadian government," the ambassador said.

The Justice and Equality Movement, or JEM, is a Sudanese rebel group. Abdalhaleem said the rebels were trying to put the Sudanese government under pressure and that Khartoum would have no interest in attacking a U.N.-AU convoy.

U.N. peacekeeping chief Jean-Marie Guehenno told the Security Council that a local commander of the Sudanese armed forces had contacted UNAMID and taken responsibility for the attack, but Abdalhaleem said this was incorrect.

JEM commander Abdel Aziz el-Nur Ashr dismissed the ambassador's accusation and said the attack was in territory controlled by Sudanese government forces.

The Sudanese ambassador said Khartoum was open to a joint investigation of the incident and criticized Ban for condemning Sudan before an investigation had been completed.

DETERIORATING SECURITY

Monday's attack, in which a Sudanese driver was shot seven times and critically injured, came at a time of heightened tension in West Darfur state and neighboring regions in Chad.

Chadian air force planes bombed Chadian rebel positions close to the West Darfur capital El Geneina on Sunday, a U.N. report said about the second reported incursion into Sudanese territory in two weeks.

Guehenno also spoke of "a dramatic deterioration of the security situation in Darfur," adding that the participation of Chadian elements made a bad situation worse.

U.S. State Department spokesman Sean McCormack said Washington "believes this incident demonstrates the need for a stronger arms embargo for Sudan and we will be working with our Security Council partners to that end."

Libyan Ambassador Giadalla Ettalhi, president of the council this month, said all 15 council members condemned the attack on UNAMID though there remained disagreement over whether Sudanese government forces were responsible.

He said council members were discussing a U.S.-drafted statement condemning the attack.

British Ambassador John Sawers criticized Khartoum for rejecting a contingent of Nordic engineers that was to be sent to Darfur as part of the full deployment of U.N.-AU forces, which is to number 26,000 compared with the present 9,000.

He said it was another example of Khartoum's "persistent obstruction and foot-dragging."

Guehenno reiterated that the peacekeepers urgently needed helicopters and other heavy transport equipment.

Both Sawers and U.S. Ambassador Zalmay Khalilzad said the United States and other countries were working on getting the U.N.-AU troops helicopters and other much-needed equipment.

International experts estimate 200,000 people have died since mostly non-Arab rebels took up arms in early 2003, accusing the central government of neglecting the remote region. Khartoum says the West is exaggerating the conflict. (Additional reporting by Andrew Heavens in Khartoum and Susan Cornwell in Washington) (Reporting by Louis Charbonneau; Editing by Xavier Briand)

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