Lawmakers pledged Sunday to study the movements of planes and ships traveling to the remote British outpost Diego Garcia amid persistent suspicion it is used by U.S. authorities to detain or transfer terrorism suspects.

Parliament's Foreign Affairs Select Committee said it plans a thorough investigation of the use of the Indian Ocean island, which hosts a U.S. military base. Britain leased Diego Garcia, which is halfway between Africa and Southeast Asia, to the United States, and in 1971 barred anyone from entering the islands except by permit.

The United States initially denied using the island for extraordinary rendition flights. However, it acknowledged in February that it had misled the British government and that two suspects had been on flights that stopped to refuel on Diego Garcia en route to Guantanamo Bay and Morocco in 2002.

Reprieve, a British human rights organization, claims the U.S. has used military ships off Diego Garcia as prisons to detain suspects in terror cases. The U.S. Navy has previously said ships elsewhere have been used to hold a few prisoners for short periods, but denied that there are long-term floating prisons.

Committee chairman Mike Gapes said the United States' initial lack of transparency makes it necessary to scrutinize "all flights and ships serviced from Diego Garcia."

"We found it deplorable that previous U.S. assurances about rendition flights through Diego Garcia had turned out to be false," he said.

The new study comes only days after British Foreign Secretary David Miliband said the United States had studied a list of 391 flights compiled by British human rights groups and lawmakers and told Britain it had found no further extraordinary rendition flights that passed through British territory.