Manouchehr Mottaki gave no other details of the probe or a possible time frame on the case. But his comments suggested that formal charges could still be possible against the Americans despite a recent pledge by President Mahmoud Ahmadinejad to request "maximum leniency" for them.

In a wide-ranging news conference, Mottaki also repeated accusations of a U.S. role in the disappearance of an Iranian scientist in June while on a pilgrimage in Saudi Arabia. Mottaki said the United States "must be held accountable" for information on Shahram Amiri but made no direct connection with the case of the American hikers.

In other comments, Mottaki increased pressure on Pakistan to crackdown on Sunni militants after Sunday's suicide attack in the border region that killed 42 people, including top commanders of the powerful Revolutionary Guard. Iran's state television on Tuesday raised the number of Guard members killed in the blast to 15.

The three Americans — Shane Bauer, Sarah Shourd and Josh Fattal — were arrested after straying over the border during a hike in northern Iraq. They have been visited by Swiss diplomats, who oversee U.S. interests in Iran.

Earlier this month, the hikers' relatives presented a petition to Iran's mission at the United Nations in New York asking for their release.

In an interview with the Associated Press last month, Ahmadinejad said he would ask the country's judiciary to expedite the process and "look at the case with maximum leniency."

The case could be complicated by Iran's demands for information on the scientist Amiri, who reportedly worked at a university linked to the Revolutionary Guard. Amiri's wife has said he was researching medical uses of nuclear technology and was not involved in the country's broader nuclear program.

Talks between Iran and other nations, including the United States, began in Vienna on Monday with proposals for Iran to allow uranium enrichment outside its borders to supply fuel for its reactor.

Mottaki claimed Amiri was "kidnapped" in a plot masterminded by Washington and assisted by Saudi officials.

Saudi officials have made no public comments on the accusations. Earlier this month, State Department spokesman Ian Kelly said he had no information about the reported disappearance, adding that "the case is not familiar to us."

Amiri traveled to Saudi Arabia on May 31 for omra, an Islamic pilgrimage to Mecca, his wife told the semi-official news agency ISNA. The last she heard from him was on June 3, when he called her from the holy city of Medina.

Mottaki also demanded that Pakistan arrest and extradite suspected members of the Sunni insurgent faction Jundallah, or Soldiers of God, which claimed responsibility for Sunday's suicide attack.

Iran claims that Pakistan aids and shelters the group, which purports to be fighting for the rights of minority Sunni tribes in southeastern Iran. On Monday, Iranian officials said the United States and Britain also have links to Jundallah — charges denied by both nations.

Pakistani authorities have promised to help Iran fight the militants but insists there is no high-level backing for the group.

Enlarge AP Undated photo released by freethehikers.org in August shows imprisoned American hikers, Shane Bauer, left, and Sarah Shourd.