BAGHDAD (AP) – A suicide bomber driving a truck loaded with TNT and toxic chlorine gas crashed into a police checkpoint in western Ramadi on Friday, killing at least 27 people and wounding dozens, police in the Anbar provincial capital said.

In the deep south of the country, the Basra police commander said the type of roadside bomb used in an attack that killed four British soldiers on Thursday had not been seen in the region previously. Maj. Gen. Mohammed al-Moussawi’s description of the deadly weapon indicated it was a feared Iranian-designed explosively formed penetrator.

Two more of the bombs were discovered planted along routes heavily traveled by U.S. and British diplomats in Basra. Weeks earlier, the American military had claimed Iran was supplying Shiite militia fighters in Iraq with the powerful weapons, known as EFPs. They hurl a molten, fist-sized copper slug capable of piercing armored vehicles.

The bombing in Anbar province marked the ninth use of suicide chlorine bombs in the sprawling, mainly desert territory that has been a stronghold of the Sunni insurgency.

Recently, however, many Anbar tribes have switched allegiance, with large numbers of military-age men joining the police force and Iraqi army in a bid to expel Al Qaeda in Iraq fighters. Suicide bombings are an Al Qaeda trademark.

Police Major Mohammed Mahmoud al Nattah, member of the Anbar Salvation council, told state-run Iraqiya television the bomber hit a residential complex and dozens of wounded were taken to the Ramadi hospital.

Police opened fire as the suicide car bomber sped toward a checkpoint, three miles west of the city, according to police Colonel Tariq al-Dulaimi. Nearby buildings were heavily damaged and police were searching the rubble for more victims.

South of Baghdad, Iraqi forces backed by American paratroopers swept into a troubled, predominantly Shiite city before dawn, and the American military said as many as six militia fighters had been killed.

Lieutenant Colonel Scott Bleichwehl, an Americanmilitary spokesman, said eight others were wounded and five detained. There were no reports of civilian casualties in the assault on Diwaniyah, he said.

Residents reported heavy fighting between American and Iraqi forces and gunmen of the Mahdi Army militia in the city, 80 miles south of Baghdad.

Dr. Hameed Jaafi, the director of Diwaniyah Health Directorate, said an American helicopter fired on a house in the Askari neighborhood, seriously wounding 12 people as the early morning assault began.

Colonel Bleichwehl said there were no American air strikes either by helicopters or planes.

Also Thursday, the American military confirmed an American helicopter carrying nine people had been downed south of Baghdad and that four were injured.

An Iraqi army official, speaking on condition of anonymity because of security concerns, said the helicopter crashed after coming under fire near the Sunni insurgent stronghold of Latifiyah, about 20 miles south of Baghdad. The American military did not confirm that account.

It was the ninth American helicopter to go down in Iraq this year. The American military has studied new evasive techniques, fearing insurgents have acquired more sophisticated weapons or have figured out how to use their arms in new and effective ways.

The four British soldiers – including two women – were killed Thursday as the American military announced the deaths of nine more U.S. soldiers since Tuesday.

The Basra region police commander, al-Moussawi, said two similar bombs had been discovered Friday morning; one was discovered on the road leading to Basra Palace, the compound that houses a British base and the British and American consulates. A second was uncovered in the western Hayaniyah district where Thursday’s attack occurred. The area is known as a stronghold of the Mahdi Army, a militia loyal to radical Shiite cleric Muqtada al-Sadr.

The reported deaths of the American forces and the bomb attack on the British unit marked the start of the eighth week of the joint American-Iraqi security crackdown in Baghdad and surrounding territory.

Prime Minister Tony Blair called the Basra attack an “act of terrorism” and suggested it may have been the work of militiamen linked to Iran. He stopped short of accusing Tehran, however.

“Now it is far too early to say that the particular terrorist act that killed our forces was an act committed by terrorists that were backed by any elements of the Iranian regime, so I make no allegation in respect of that particular incident,” Mr. Blair said.

He added, however, “This is maybe the right moment to reflect on our relationship with Iran.”

The American military reported Saturday that one American soldier was killed and a second wounded in shooting in Kirkuk province.

One American soldier died and two were wounded in a roadside bombing Thursday in restive Diyala province north of Baghdad, the military said. Four others died Wednesday in two roadside bomb explosions in southern Baghdad and north of the capital, while a fifth was killed by small-arms fire in the eastern part of the city. Two other soldiers were killed by small-arms fire on Tuesday – one in eastern Baghdad and another on foot patrol in the southern outskirts of the capital.