BAGHDAD (AP) – American forces broke up a Shiite militant cell believed to be smuggling an armor-piercing Iranian weapon responsible for killing an increasing number of Americans and Iraqis, the military said. Separately, the U.S. announced the deaths of five American soldiers and an Iraqi interpreter.

Roadside bombs were responsible for three of the American deaths announced Friday and have long been the No. 1 killer of American and Iraqi forces in Iraq, but the use of the Iranian explosively formed penetrators, or EFP’s, is rising. The weapons, which hurl a fist-sized lump of molten copper, can pierce even American armored vehicles newly designed to deflect roadside bombs.

In Sadr City, the Baghdad slum that is home to Shiite militias allied with radical anti-American cleric Muqtada al-Sadr, coalition raids rounded up 16 suspected members of a militant cell that brought in the Iranian weapons, as well as militants seeking terrorist training, America said. Intelligence reports also indicate the cell is linked to kidnappings in Iraq, the statement said.

The military said over the last six months American forces have found and destroyed four caches of Iranian-linked weapons around Mahmoudiya, a mostly Shiite enclave surrounded by Sunni-dominated areas about 20 miles south of Baghdad. Sectarian violence and attacks by militias and insurgents on American and Iraqi forces are common in the area.

Iranian officials deny importing weapons or militants into neighboring Iraq, but The Washington Post reported Friday that attacks in Iraq involving Iranian-made EFPs reached a record high last month.

Quoting Lieutenant General Raymond T. Odierno, who oversees day-to-day American military operations in Iraq, the paper said the number of attacks with the projectiles rose to 65 in April, most of them in predominantly Shiite eastern Baghdad. Officials said the projectiles are used almost exclusively by Shiite fighters against American military targets.

EFPs were first reported used in Iraq in 2005 against British forces in the south, but have grown increasingly common, primarily in Baghdad.

The Post quoted General Odierno as saying that before April, the month with the greatest number of projectile attacks was December 2006, with 62. It said the use of projectile weapons has risen over time as other types of bombs have become less effective against added American armor.

Overall attacks using roadside bombs doubled in Iraq from 2006 to 2007 and number about 1,200 a month, the Post said. They cause roughly 70 percent of the casualties suffered by American troops, the paper said.

Roadside bombings on Friday killed an American soldier and, separately, five Iraqi policemen. Elsewhere in the capital on Thursday, roadside bombs killed two American soldiers and an Iraqi interpreter. Two other American soldiers were killed Thursday in fighting in Anbar province.

Seprately, seven bodies were found floating in the Diyala River in Baqouba, 35 miles northeast of Baghdad, and snipers were preventing police and medical teams from recovering from the remains along with other bodies spotted in recent weeks from the waterway, police said.

Also Friday, the American military identified two more top al-Qaida aides killed earlier this week targeting Muharib Abdul-Latif al-Jubouri, a senior propagandist for the terror network.

The American operation north of Baghdad led to days of conflicting reports from the Iraqi government that the leaders of Al Qaeda and its front group, the Islamic State of Iraq had been killed.

The chief American military spokesman on Thursday said America did not have the bodies of Al Qaeda boss Abu Ayyub al-Masri or Islamic State leader Abu Omar al-Baghdadi and did not know “of anybody that does.”

The military on Friday identified two of the other slain militants as al-Jubouri’s spiritual guide Sabah Hilal al-Shihawi and a foreign fighter, Abu Ammar al-Masri, who it said was helping with insurgent activity and infrastructure support for Al Qaeda.

Lt. Col. Christopher Garver, another American military spokesman, said Friday that Abu Ammar al-Masri is unrelated to the Al Qaeda boss.