Coalition troops in Iraq found a torture house with five skeletons and 40 nuclear, biological and chemical weapons masks, a U.S. general told FOX News on Thursday.

Brig. Gen. James Boozer said forces found execution equipment and chains in the house in the Diyala River Valley, an Al Qaeda stronghold north of Baghdad, as he touted progress in bolstering Iraqi security forces and said Iran seems to be holding to a commitment to thwart the flow of weapons into Iraq.

"I think we're at here an historical point in the history of Iraq," said Boozer, commander of Multi-National Division-North in Iraq.

Boozer said it appears Iran is keeping its promise to Iraqi leaders to helping stop the flow of roadside bombs into Iraq, which has contributed to a decrease in attacks.

"We've seen no increase in or any indication that the Iranians have stepped up the influx of arms or weapons into Iraq. It looks like they are holding up to their agreement," he said.

In August, Tehran vowed to Iraqi Prime Minister Nouri al-Maliki to hinder the smuggling of those weapons, called explosively formed penetrators, or EFPs, and ammunition into the hands of extremists.

Maj. Gen. James Simmons, a deputy corps commander, said that in October, U.S. forces logged 1,560 cases in which bombs were either found and exploded.

That compared with 3,239 incidents in March, he said. The October figure was the lowest since September 2005, he added.

"We believe that the commitments that the Iranians have made appear to be holding up," Simmons said.

Iranian officials have publicly denied smuggling weapons to Shiite extremists. But U.S. authorities insist penetrator bombs are the signature weapon of Shiite militants.

"There has been, as you know, some finding of some EFP devices, some Iranian arms and ammo in some of these cache sites that we've uncovered," Boozer said. "But it is hard to determine when they got there and how long they've been there."

U.S. authorities said penetrators were used in an attack on Wednesday against a U.S. Stryker vehicle near an entrance to the Green Zone, killing an American soldier and wounding five others. Iraqi police said two Iraqi civilians also were killed.

It was the first major attack against a U.S. military vehicle in that area in the last four or five months, Simmons said.

He said the vehicle was struck by "an array" of penetrators. The attack occurred in one of the most heavily protected areas of the capital, raising questions about how the explosives could have been planted without collusion from Iraqi police or soldiers.

The general said U.S. and Iraqi authorities were investigating.

Simmons said U.S. authorities also were encouraged by an increase in tips from Iraqi citizens about weapons caches, which he interpreted as a sign the public was turning against both Shiite and Sunni extremists.

"We had found more caches by May of this year than in all of 2006," he said.

Simmons said most of the roadside bomb attacks recently had occurred in Sunni areas north of Baghdad.

Northern Iraq also has seen a spike in violence in recent months as extremists were pushed from strongholds in and around Baghdad.

In Kirkuk, an ethnically mixed city 180 miles north of Baghdad, a homicide bomber rammed his car into a police patrol in Kirkuk, killing six people and wounding more than 20, said police Brig. Sarhad Qadir.

The city has seen a rise in bloodshed ahead of a planned census and referendum to determine the future of the city — whether it will join the semiautonomous Kurdish region on its border, or remain under Baghdad's control.

The bomber's apparent target was the six-car convoy of a senior Kurdish police officer, Brig. Gen. Khattab Omar, who heads the city police department's quick response force, Qadir said.

Three of Omar's officers were killed, along with three civilians, but the commander survived with serious injuries to his chest and head, Qadir said. Omar was being evacuated to a larger hospital, he said.

Video from AP Television News showed a charred Iraqi Humvee being towed from the scene.

Many of the 21 people wounded were children who had been walking to school when the bomber struck. APTN video from inside a nearby hospital showed a young girl in a school uniform, drenched in blood. A child's shoe could be seen peeking out from under a tarp covering corpses — suggesting at least one of the dead civilians was a child.

Also Thursday, the U.S. military said a U.S. soldier had been killed a day earlier in an explosion in Diyala province that wounded four other soldiers.

At least 3,865 members of the U.S. military have died since the beginning of the Iraq war in March 2003, according to an AP count.

Meanwhile, Iraqi officials said they were investigating whether U.S. troops had mistakenly killed about two dozen anti-Al Qaeda fighters earlier this week north of Baghdad.

FOX News' Jennifer Griffin and The Associated Press contributed to this report.