By Claudia Parsons

UNITED NATIONS, Dec 13 (Reuters) - Sudan's failure to approve some non-African units of a U.N.-African peacekeeping force for Darfur is delaying preparations for its Jan. 1 deployment, a U.N. official warned on Thursday.

Deputy peacekeeping chief Edmond Mulet briefed the Security Council on weekend talks with Sudanese officials aimed at persuading Khartoum to approve a list of troop contributors that includes units from Thailand and Nepal, as well as an engineering unit from Nordic countries.

Mulet said there had been some progress on technical issues, but Khartoum had not responded on the Thai, Nepalese and Nordic units.

"This is delaying the putting in place of many of the other assets," he said. "This is an answer we need urgently."

On Jan. 1, the joint U.N.-African Union force is due to take over from an existing AU force of just 7,000, which has been unable to stop a conflict that has raged for 4-1/2 years.

But no country has offered the 24 helicopters requested by the United Nations. Without them the peacekeepers will be unable to move around an are about the size of France or defend themselves if they come under attack, U.N. officials say.

Mulet said Sudan had agreed to accept helicopters from any country identified by the United Nations and the AU. Asked if that would include the United States, which Sudan has said it would not accept, Mulet did not comment.

Diplomats say states that could contribute the 18 transport and six attack helicopters required have been reluctant either because they have none to spare or because they are unhappy about the new force's command and control arrangements.

U.N. Secretary-General Ban Ki-moon said last week he had personally contacted every possible contributor.

U.S. Ambassador Zalmay Khalilzad said he was not aware of a direct request to Washington to provide helicopters but Ban had made a general request to all countries. Washington already provides air-lift and has paid for the construction of camps for Darfur peacekeepers.

Asked about possible Sudanese objections to U.S. helicopters, Khalilzad said Washington was "engaging other governments to see where the capabilities are available."

But he said Sudan could not be allowed to refuse what the U.N. Security Council and the African Union requested.

"We can't allow a set of precedents, (that) you can pick and choose, you will take assets, assistance from country X but not from country Y," Khalilzad said.

Khalilzad said there had been limited progress on the technical issues but Sudan must implement its commitments.

"There has been a record of the Sudanese government dragging its feet to come to agreement and dragging its feet in implementing agreement," he told reporters. (Editing by Chris Wilson)

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