Defense Secretary Donald H. Rumsfeld said Tuesday that weapons have been found in Iraq that were "clearly, unambiguously" from Iran and that the weapons would ultimately become a problem for Tehran.

Speaking at a Pentagon briefing with Air Force Gen. Richard B. Myers, chairman of the joint chiefs of staff, Rumsfeld said it was unclear whether the weapons were coming from elements of the Iranian government or from other parties in that country.

"What you do know is that the Iranians did not stop them from coming in," he told reporters. "It's notably unhelpful for the Iranians to be allowing weapons of those types to cross the border," said Rumsfeld. He offered no further specifics on the weapons.

He said the weapons were "a problem for the Iraqi government, for the coalition forces, for the international community and ultimately it's a problem for Iran."

Asked if his comment constituted a threat against Tehran, Rumsfeld said no, and then replied: "They [the Iranians] live in that neighborhood. The people in that region want that situation stabilized, with the exception of Iran and Syria." He made no further mention of Syria.

At the briefing, the Pentagon also announced that Iraqi and U.S. forces have arrested suspects in Haditha, Iraq, in the deaths of 20 U.S. Marines in two incidents last week.

Myers said the arrests showed that Iraqi civilians were against the insurgents and cooperating with the U.S.-led coalition in the country.

"The public came forward and said, 'These are the folks,' " Myers said at the briefing. He did not say how many people had been detained or identify them further.

Six Marine snipers were killed by small arms fire on Aug. 1 in Iraq's far western Anbar province. Two days later, a Marine armored personnel carrier rolled over an explosive device in the same area, killing 14 Marines from one unit in Ohio and their Iraqi civilian translator.

Myers said the explosives used in the attack were three stacked landmines.

"It doesn't require a big hole," Myers said of the mines. "It was a small device placed in the road."

Rumsfeld warned that there may be more deadly attacks in Iraq as Iraqi factions draft and ratify a new constitution in the weeks and months ahead. He said stepped-up attacks did not mean the insurgents were winning, however, and that one should be careful not to "draw the wrong conclusions."