Sudan has repeated its opposition to replacing an African Union force in Darfur with U.N. peacekeepers.

Jendayi Frazer arriving in Khartoum

A Sudanese government spokesman aid Khartoum's position was put forward during a meeting Tuesday between President Omar al-Bashir and visiting U.S. envoy Jendayi Frazer.

Frazer delivered a message from President Bush urging Sudan to accept a U.N. force. She had been initially scheduled to wrap up her trip to Sudan on Monday, but was forced to extend her stay in Sudan after Mr. Bashir, who cited a busy schedule, refused to meet her for several days.

U.S. officials in Washington said they remain optimistic that Sudan, despite its stated objections, will accept the conversion of the AU mission into a full-scale United Nations peacekeeping operation.

The State Department says Mr. Bashir promised to send an envoy to Washington to discuss the issue.

Meanwhile, Britain and the United States have called for a vote on a U.N. draft resolution to allow the United Nations to begin assembling a mission for Darfur.

Diplomats say the resolution will not allow U.N. troops to actually enter Darfur until Sudan approves such a move.

On Monday, Sudan refused to participate in a meeting of the U.N. Security Council where members discussed the resolution.

Some information for this report was provided by AFP, AP and Reuters.