About 20 people suspected of having connections to Al Qaeda have been arrested by the U.S. military in Iraq, the commander of American forces there said Tuesday.

"At one point, we had up to about 20 suspected Al Qaeda members," Lt. Gen. Ricardo Sanchez (search) told reporters, "but as we have continued to refine and interrogate, we have not been able to establish definitively that they were Al Qaeda members."

Sanchez did not say where the suspects were captured or being held, when they were detained or whether any had been released.

U.S. officials are fairly certain that anti-American foreign volunteers, some with links to Al Qaeda or other militant Islamic groups, have been slipping into Iraq to participate in a "jihad," or holy war, against the U.S.-led occupation. But the number of "jihadis" and their roles in attacks on coalition forces is still unclear.

Sanchez emphasized the possible connections to Al Qaeda to reporters Tuesday. 

"We believe that there is in fact a linkage," he said, "if nothing more than, of course, ideology, and then also some training and possibly some financial linkages that exist to the international terrorist groups."

Asked about numbers of foreign fighters, Sanchez said "hundreds" of foreigners cross the border area to carry out attacks in Iraq. Asked how close U.S. forces had been to capturing Saddam Hussein, Sanchez replied only: "Not close enough."

American commanders have speculated that they are facing attacks from Saddam supporters, religious extremists and foreign fighters. U.S. officials have said at least some of the attacks may have been orchestrated by Saddam's former deputy Izzat Ibrahim al-Douri (search), who may have forged an alliance with the Kurdish religious extremist group Ansar al-Islam (search).

Ansar al-Islam is believed to have ties to Al Qaeda. It was unclear whether Sanchez was referring to Ansar fighters when he said the Americans were holding about 20 Al Qaeda suspects.

Sanchez said there was "no doubt" that the insurgency had intensified and that the guerrillas "have developed their capability" employing rockets and mortars in recent attacks.

Sanchez said most of the foreign fighters enter the country from Syria and across the northeastern border with Iran. He said Iraqi immigration authorities were now monitoring the borders more effectively to make sure no one entered the country with forged documents.

The Associated Press contributed to this report.