The US State Department said on Monday Washington was not impressed with Tehran's weekend announcement that it had provided the United Nations with the names of scores of suspected al-Qaida members in its custody.
"We believe Iran needs to turn over all suspected al-Qaida operatives to the United States, or to their countries of origin, or to third countries for interrogation and trial," said spokesman Richard Boucher.
"It's essential that other countries have direct access to information that these people may have about past and future al-Qaida activities," he said.
The US has been increasing diplomatic and political pressure on Iran's clerical leadership in recent months over several issues, including the latter's nuclear energy programme and its support for Palestinian resistance groups.
On Saturday, state media reported Iran had identified to the UN Security Council 78 al-Qaida suspects whom Tehran said had already been extradited to their countries of origin.
The US holds hundreds of al-Qaida
suspects at Guantanamo Bay
In addition, Iran said it had provided the names of 147 suspected members of al-Qaida - or of its former Afghan hosts, the Taliban government - who remain in custody pending trial, extradition or deportation.
Previously, Iran said it had arrested and deported about 500 people belonging to or linked to al-Qaida since late 2001.
Those who had been extradited were not believed to have included any senior members of the group.
But the identity of those still being held has been the subject of intense speculation.
Diplomatic sources and Arab press reports have pointed to the possible presence in Iran of the movement's spokesman, Sulayman Abu Gaith, and its number three, Saif al-Adl.
Also said to be in Iran is Usama bin Ladin's son, Saad, said by the US to be playing a top role in al-Qaida.
Boucher would not comment on that speculation, but noted that the Iranians themselves "have previously stated that (those held) include senior al-Qaida officials".
"We remain concerned by reports that additional al-Qaida members remain in Iraq," he said.