BAGHDAD (AP) – A suspected al-Qaida in Iraq suicide bomber smashed a truck loaded with TNT and toxic chlorine gas into a police checkpoint in Ramadi on Friday, 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 on 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, according to 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.

In the Internet feud, the Islamic Army in Iraq gave a rare glimpse of deep discord inside the Islamic State of Iraq, an umbrella organization for militant groups.

In a Thursday posting, the Islamic Army charged that al-Qaida – a key group inside the Islamic State – was killing fighters of the Islamic army and other militant Sunni groups if they did not pledge loyalty to al-Qaida.

It also charged that al-Qaida had killed Harith Dhaher al-Dhari, a field commander of the 1920 Revolutionary Brigades, another organization under the Islamic State umbrella.

“All Sunni people have become targets for them (al-Qaida), especially the wealthy. They either have to pay or be killed. Anyone who criticizes al-Qaida or disagrees or points out its mistakes is killed,” the posting said.

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 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. 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.

On Thursday, 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, but he stopped short of issuing an outright accusation against Tehran. The British were killed the same day Iran released a captured British navy crew that was held for nearly two weeks for allegedly straying into Iranian waters.

Reflecting on that incident and the deaths of the British soldiers, Bruce Riedel, a scholar at the Brookings Institution Saban Center, said Tehran was flexing its muscle to show both Britain and America that it could strike at will.

“They have identified the British forces in Iraq and in the Gulf as a prime vulnerability,” Riedel said. “I don’t think I can prove it, but I think it’s very interesting that in the last 100 hours six British soldiers have been killed by Shiites in Basra.”

Britain lost two other soldiers this week, one on Sunday and a second on Monday.

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.

Residents reported heavy fighting between the U.S. 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 assault began.

Lt. Col. Scott Bleichwehl, a military spokesman, said there were no U.S. air strikes either by helicopters or planes.