BAGHDAD (AP) – A suicide bomber walked into an Iraqi army recruiting center outside of Baghdad on Saturday and blew himself up amid a crowd of recruits, killing at least 15 people and wounding 22 others, police said.

The attack underscored the danger facing Iraqi forces who are frequently targeted by Sunni insurgent groups that accuse them of collaborating with U.S.-led efforts to stabilize the country.

The explosion hit about 10 a.m., when the bomber entered a recruitment center in Abu Ghraib, a town on the western outskirts of the capital, police said. Witnesses said guards spotted the bomber but were unable to stop him from detonating his explosives vest.

Nobody claimed responsibility for the attack, which killed five soldiers and 10 recruits, police said.

In a separate incident, five Iraqi police officers were discovered shot, killed and dumped in a deserted field outside the city of Beiji, 250 kilometers (155 miles) north of Baghdad late Friday, police said Saturday.

The bullet-riddled bodies of the five police officers were dressed in civilian clothes. Their identity documents showed they were from the turbulent city of Ramadi, police said.

The attacks occurred as Al-Qaeda in Iraq released a recording purportedly of its leader, who had been reported killed in recent fighting, criticizing the country’s largest Sunni party and branding its chief, Vice President Tariq al-Hashemi, a “criminal” for participating in the government.

The statement by Abu Hamza al-Muhajir, also known as Abu Ayyub al-Masri, was seen as a warning to Sunnis not to take part in the political process that could legitimize the Shiite-led government and its U.S. backers.

Al-Hashemi has resisted calls by fellow leaders of the main Sunni alliance to pull out of the government.

The al-Masri statement, posted on a militant Web site, did not directly address reports from Iraqi officials that the al-Qaeda leader was killed Tuesday by rivals north of Baghdad.

The U.S. military declined to confirm the report of al-Masri’s death and believed it stemmed from confusion over the killing of another al-Qaeda militant.

There was no indication when the 20-minute statement released Saturday was recorded, although a transcript posted on the Web site was dated Saturday. It could not be independently verified.

Al-Masri, an Egyptian militant, took over leadership of the terror network after Abu Musab al-Zarqawi was killed in June by a U.S. airstrike.

In the statement Saturday, al-Masri sharply criticized al-Hashemi for taking part in politics and legitimizing the Shiite-led government of Prime Minister Nouri al-Maliki, whose U.S.-backed security forces are fighting Sunni insurgents and al-Qaeda militants.

“This criminal relentlessly calls for the occupier to remain,” he said, referring to al-Hashemi.

Last week, al-Hashemi spoke to U.S. President George W. Bush in a phone call to discuss the Sunni threats to leave the Cabinet.

An insurgent statement in March, calling Deputy Prime Minister Salam al-Zubaie a stooge “to the crusader occupiers,” was followed a day later by an assassination attempt against the highest-ranking Sunni government official. That statement, which was made by the al-Qaeda front group, the Islamic State of Iraq, also singled out al-Hashemi.

The latest statement, however, did not calling for attacks against the Islamic Party, which, al-Masri said, would only distract his group from its fight against the Shiites and American forces. “The leaders of the Islamic Party are renegades but we make it clear that we don’t want to fight them and be drawn into secondary battles that only serve the occupier and its Shiite associates,” he said.

Violence persisted throughout the country. Residents and police in a Shiite area in eastern Baghdad said U.S. helicopters early Saturday fired on three houses, killing six men and wounding a woman and five children. The U.S. military said a helicopter supporting ground operations in the area was attacked with small-arms fire but “did not return fire.” AP Television News footage showed a shattered wall of one house and a satellite dish punctured by large holes apparently caused by artillery. Dozens of people marched in a funeral procession for four of those killed, bearing their bodies in wooden coffins draped with Iraqi flags.

In all, at least 40 people were killed or found dead in scattered violence. Those included a policeman killed in a suicide car bomb attack and a woman who died in a mortar attack in Baghdad, as well as three people killed in clashes between Shiite and Sunni militants north of the capital.

In southern Baghdad, U.S. soldiers on a routine patrol Friday searched a suspicious blue tanker truck and discovered it had been converted into a large truck bomb, the military said.

The explosive on the truck consisted of 14 155 mm artillery shells and was destroyed by a team of bomb disposal experts, the military said Saturday. In an effort to prevent further attacks on troops, U.S.-led forces arrested suspected Shiite militants accused of smuggling powerful bomb components from Iran during a raid Friday in Baghdad’s teeming Shiite district of Sadr City.

A U.S. military statement said the militants were part of a “secret cell” that smuggles powerful bombs known as “explosively formed penetrators,” or EFPs, from Iran and sends Shiite fighters from Iraq for training in Iran. U.S. and some Iraqi officials suspect the Iranians may be stoking a growing power struggle among Shiite factions and political parties, despite the Tehran government’s insistence that it is working to help bring stability to its neighbor Iraq.