The U.S. State Department's No. 2 official will travel to Libya later this month, the highest ranking American diplomat to visit the country since 1953.

Deputy Secretary of State John Negroponte will go to Tripoli as part of a four-nation Africa tour that also will include Sudan, Chad and Mauritania.

Spokesman Sean McCormack said the trip's focus will be the ongoing humanitarian crisis in the Darfur region of Sudan, which shares a border with Libya. The government of Libyan leader Moammar Qadaffi has facilitated delivery of humanitarian relief to Darfur through Libyan territory.

The highest ranking U.S. official ever to visit Libya was Secretary of State John Foster Dulles 54 years ago.

Qadaffi's decision in 2003 to dismantle his nuclear weapons program was a major breakthrough in U.S.-Libyan relations. Mid-level U.S. officials have visited Libya but, because of ongoing disputes, Secretary of State Condoleezza Rice has not been able to accommodate Libyan wishes that she travel there.

One purpose of a Rice visit would be to inaugurate the new U.S. embassy in Tripoli. The embassy opened last year but there was no ceremony to mark the occasion.

One dispute with Libya involves its refusal thus far to make the final payment on the $270 million in compensation it promised to give families of the victims of the Pan Am 103 bombing over Lockerbie, Scotland in 1988.

Also, Libya has ignored U.S. calls for the release of five Bulgarian nurses and a Palestinian doctor who have been sentenced to death after being convicted on charges that they deliberately injected hundreds of Libya children with the AIDS virus. The case is under appeal.

Last week, Qadaffi upset U.S. officials when he derided Arab leaders attending a summit in Saudi Arabia, accusing them of following American orders.