UNITED NATIONS (AP) _ Libya has asked the U.N. chief to clarify where two suspects in the 1988 Pan Am Lockerbie bombing would serve their sentences if convicted, a diplomatic source said.

The Libyan concerns about a proposal to try the two suspects were contained in a letter presented to Secretary-General Kofi Annan by the Libyan foreign minister, Omar al-Muntasser, at a summit last week of developing nations in South Africa.

Annan passed along the letter to his legal advisers, who were conferring about how to address Libyan questions. Among the concerns was where the men would serve their sentences and questions surrounding the testimony of witnesses, a diplomatic source familiar with the letter said Friday. He spoke on condition of anonymity.

A suitcase bomb exploded on board Pan Am Flight 103 over Lockerbie, Scotland, killing 270 people on board and on the ground.

A U.S.-British proposal, made last month in a bid to bring justice to the 10-year-old case, calls for the two suspects to be tried at a court in the Netherlands by Scottish judges according to Scottish law.

The proposal, which was backed by a Security Council resolution, calls for the men to be imprisoned in Britain if convicted. The Tripoli government has said it wants the men imprisoned in Libya if convicted.

Earlier this week, Annan told reporters that Al-Muntasser had confirmed to him that they were prepared to comply with the council's decision.

``But the details, the fine print _ there are certain things in the fine print _ they would want some clarification on,'' he said.

The proposal called on Annan to provide the Libyans with any clarifications they needed and to assist in the transfer of the two suspects for trial.

The Security Council has agreed to suspend economic sanctions imposed on Libya once it turns over the two men.