Three American soldiers were killed Wednesday in the Sunni insurgent area west of Baghdad, and Iraqi officials said about 1,500 people died violently last month in the capital alone — many shot execution-style by sectarian death squads.

The soldiers were assigned to the 1st Brigade, 1st Armored Division, a U.S. statement said without elaboration. The brigade operates around Ramadi, capital of Anbar province where support for the Sunni insurgency is strong.

In addition, two U.S. troopers were missing Wednesday after a UH-60 Blackhawk helicopter went down the day before in Anbar province.

The helicopter crashed in an unspecified body of water and divers were searching for the missing troops, a U.S. spokesman said. The crash was not due to hostile fire, the U.S. said.

The latest deaths brought to at least 17 the number of American service members killed in Iraq this month. All but five of them died in Anbar, indicating the ongoing threat from Sunni insurgents at a time when attention has been focused on sectarian violence between Sunnis and Shiites in Baghdad.

On Wednesday, deputy Health Minister Dr. Sabah al-Husseini said about 1,500 violent deaths were reported last month in the Baghdad area — excluding members of the U.S.-led coalition.

The assistant manager of the Baghdad morgue, Dr. Abdul Razzaq al-Obeidi, said 1,815 bodies were brought in last month, and about 85 percent of them had died violently. The biggest cause of violent deaths was gunshot wounds, mostly in the head, he told The Associated Press.

Head shots are generally associated with death squads that roam neighborhoods of the capital seeking victims from the rival Muslim sect. Violence between Shiite and Sunni extremists has been surging since the Feb. 22 bombing of a Shiite shrine in Samarra.

Four people were killed and five wounded when fighting broke out late Wednesday between gunmen and residents of a Shiite community in north Baghdad. police Lt. Salim Ali said. Sporadic clashes were continuing in the area, he said.

Four people were killed and 16 wounded in an explosion late Tuesday at a Shiite mosque in downtown Baqouba, a religiously mixed city 35 miles northeast of Baghdad. Several nearby buildings were damaged in the blast.

In a statement Wednesday, the Shiite Endowment, which takes care of Shiite shrines across the country, blamed "terrorists" for the blast and demanded that government security forces protect places of worship in the area — scene of numerous car bombings, kidnappings and armed attacks by Sunni and Shiite extremists.

The sharp rise in sectarian violence has dashed U.S. hopes that the installation of a government of national unity would set the stage for a significant drawdown in the 127,000-strong U.S. military force here.

Instead, the U.S. military is rushing 12,000 American and Iraqi soldiers into Baghdad to regain control of the streets from Sunni insurgents, Shiite militiamen, criminals and freelance gunmen.

U.S. officials have refused to say how many reinforcements have arrived so far in the capital, although some of them have been seen patrolling a tense Sunni neighborhood in the west of the capital.

Maj. Gen. William Caldwell told reporters Wednesday that the buildup would take place gradually and that the new operation needed the cooperation of the Iraqi public to succeed.

"They have to be involved. The Iraqi people have to want this to work. If they are not involved ... then there is no solution," Caldwell said.

Caldwell's appeal reflects the private frustration of some U.S. officials that the Iraqi public is reluctant to provide information on gunmen hiding in their neighborhoods.

More significantly, many of the sectarian militias responsible for the violence are linked to political parties that are part of Prime Minister Nouri al-Maliki's government, which took office May 20.

Some U.S. officials have said Iraqi commanders themselves are frustrated over what they consider a lack of support from civilian politicians.

Al-Maliki, a Shiite, strongly criticized a U.S.-Iraqi raid Monday on a Shiite neighborhood of eastern Baghdad in which three people were killed. The raid was directed at the stronghold of the Mahdi Army militia of radical cleric Muqtada al-Sadr, a close ally of the prime minister.

On Wednesday, Caldwell defended the operation, saying U.S. and Iraqi forces tried to avoid civilian casualties and escalated the use of force only after drawing heavy fire from gunmen in the area.

Caldwell said "these death squads, the anti-Iraqi elements" were hiding "within the civilian population" to make it difficult "to get to them without inflicting casualties on civilians."

"They know exactly what they're doing by where they're placing themselves," Caldwell said.

In other developments Wednesday:

—A senior army official was assassinated in the southern city of Basra, and a roadside bomb apparently targeting a U.S. patrol killed a bystander in Baghdad.

—Police also found the bodies of three men who were shot in the head and dumped in two locations in southwestern Baghdad.

—Romanian President Traian Basescu arrived in Baghdad to meet Iraqi and U.S. officials and visit some of the country's 890 troops stationed here.