CAIRO, Egypt -- Libya will hand over to the United Nations by April 6 two suspects in the 1988 bombing of an American jetliner over Scotland, South African President Nelson Mandela said.

Libya made the promise in a letter to U.N. Secretary-General Kofi Annan, Mandela said in Tripoli, the Libyan capital. The South African leader disclosed the agreement during a speech to Libyan politicians that was broadcast by state television and monitored in Cairo.Reading from the letter as Libyan leader Moammar Gadhafi looked on, Mandela said Libya had agreed to "ensure that the two suspects would be available for the secretary-general of the United Nations to take custody of them on or before 6 April 1999."

Libya also affirmed that the suspects, if convicted, would serve any prison sentence in Scotland under U.N. supervision, Mandela said, quoting the text.

The letter also insisted the sanctions on Libya, imposed in 1992 to pressure Tripoli to turn over the suspects, would be lifted within 90 days of a report by Annan that Libya had fulfilled U.N. Security Council requirements.

Mandela said the deal on the hand-over was worked out with the help of Saudi Arabia's King Fahd and Crown Prince Abdullah.

"We are hopeful that these undertakings would (allow) the secretary-general to expedite his report to the Security Council to have sanctions against Libya finally and fully lifted," he said.

He said, "King Fahd and I take responsibility for our part in that decision" to make the contents public before the letter is delivered.

"We, the leadership of Saudi Arabia and South Africa, put our honor before you as guarantee of the good faith" of the promises made by Britain, the United States and the Security Council, he added.

Britain and the United States have agreed to comply with the Security Council's pledge to suspend the sanctions on Libya.