Baghdad, Iraq ? A suspected al-Qaida in Iraq suicide bomber smashed a truck loaded with TNT and toxic chlorine gas into a police checkpoint Friday in Ramadi, killing at least 27 people – the ninth such attack since the group’s first known use of a chemical weapon in January.

Al-Qaida in Iraq, which asserts fealty to Osama bin Laden, was believed to be hitting back at Sunni tribesmen who are banding together to expel foreign fighters from their territory.

An Internet posting by the Islamic Army in Iraq, meanwhile, exposed a growing and deep split among even the most radical Sunni groups, which are linked under the umbrella organization called the Islamic State of Iraq.

Including those killed in Ramadi, 46 people died or were found dead in sectarian violence nationwide Friday.

The bombing in Ramadi, the capital of Anbar province and an insurgent stronghold, left many people nearby with breathing difficulties and some needed hospitalization, said police Maj. Jubair Rashid al-Nayef. Most were released in about 30 minutes.

Thirty other victims were hospitalized with wounds from the explosion.

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

The first known chlorine attack took place Jan. 28, also in Ramadi. Pentagon officials first disclosed the attack, which killed at least 16 people. In low exposures, chlorine irritates the respiratory system, eyes and skin. Higher levels can lead to accumulation of fluid in the lungs and other symptoms. Death is possible with heavy exposure, according to the U.S. Centers for Disease Control and Prevention.

The U.S. military reported the death of a 20th service member so far this month – a soldier killed in a shooting Thursday in Kirkuk province. The military said the incident was under investigation, indicating the soldier did not die in combat. Spokesman Lt. Col. Michael Donnelly said he could give no further details.

An average of four soldiers have died or been killed in each of the first five days of the month. If that pace were to continue, the monthly toll would be 120 and the highest since November 2004, when U.S. forces were besieging Fallujah, then another Anbar province insurgent stronghold.

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 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. The bombs hurl a molten, fist-sized copper slug capable of piercing armored vehicles.

Al-Moussawi said two similar bombs were discovered Friday morning; one was found on the road leading to Basra Palace, the compound that houses a British base and the British and U.S. 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.

Nearer to Baghdad, Iraqi forces backed by American paratroopers swept into a troubled, predominantly Shiite city before dawn and killed three militia fighters, the U.S. military said. Twenty-seven militants were captured and two Iraqi and one U.S. soldier suffered wounds.