BAGHDAD, Iraq (AP) – U.S. troops have arrested four Iraqi men in the kidnapping of American journalist Jill Carroll, who was freed in March after 82 days in captivity, a U.S. spokesman said Wednesday.

Maj. Gen. William Caldwell said the four, who were not identified, were arrested in Anbar province west of Baghdad but he did not say when. Another U.S. official, Lt. Col. Barry Johnson, said the arrests were made about a month ago.

The military also said a U.S. Army helicopter crashed in Iraq’s western Anbar province Tuesday, leaving two crew members missing and four injured. It did not appear the helicopter was shot down, the military said.

The UH60 Black Hawk helicopter with six people aboard went down during a routine flight to survey the area, the U.S. command said Wednesday in a statement. The four injured troops were in stable condition.

Caldwell said Carroll, who works for the Christian Science Monitor, was held at three locations, including one about seven miles west of Fallujah before she was freed March 30.

The 28-year-old journalist was kidnapped Jan. 7 in west Baghdad and her Iraqi interpreter was shot dead. She was released near a Sunni Arab political party office in Baghdad and returned to the United States on April 2.

The breakthrough came after a Marine lieutenant from the 1st Marine Expeditionary Force identified a house from intelligence reports and photographs that he had seen earlier.

“Sound intelligence was paramount here,” Caldwell said.

The lieutenant and others in his unit knocked on the door of the house, asked the owner’s permission to look around and saw “very distinct features” that led them to believe it was likely one of the places Carroll had been held, Caldwell said.

The owner of the house was detained.

“After questioning that suspect, Marines identified additional locations where Jill Carroll was believed to have been held,” Caldwell said.

Caldwell said Marines from the 1st Battalion, 25th Marine Regiment, went to a second location and arrested one person. Three others were arrested at yet another place north of Abu Ghraib in a raid by the U.S. Army’s 4th Infantry Division and two hostages were freed.

During the news conference he showed a video and photographs taken by the Marines of one the homes where Carroll was believed to have been held. The house had a green gate and floral designs on its green door, while one of the rooms shown inside had little furniture besides a television, a bed, an electric fan and a water cooler.

Four of the detainees were arrested for involvement in Carroll’s kidnapping. The role of the fifth suspect was unclear. “U.S. and Iraqi authorities are currently discussing prosecutorial options and will make the determination shortly,” Caldwell said.

The Christian Science Monitor said it was aware of the announcement in Baghdad and expressed gratitude for U.S. efforts to win her release.

“Like reporters everywhere, we are reassured to hear that several of those believed to have held Jill have been apprehended,” editor Richard Bergenheim said. “The daily threat of kidnapping in Iraq remains acute for all. Everything possible needs to be done to relieve Iraqis and others of this scourge.”

The kidnappers, a formerly unknown group calling themselves the Revenge Brigade, had demanded the release of all female detainees in Iraq, saying Carroll would be killed otherwise. U.S. officials did release some female detainees but said the decision was unrelated to the demands.

In other violence 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.

In New Zealand, the Foreign Ministry said a Cook Islands national working as a driver in Iraq was killed in a bomb attack late Tuesday.

About 1,500 violent deaths were reported in the Baghdad area last month, deputy Health Minister Dr. Sabah al-Husseini said Wednesday, providing figures that showed a steady increase in killings since the beginning of the year. Those figures did not include members of the U.S.-led coalition.

The assistant manager of the Baghdad morgue, Dr. Abdul Razzaq al-Obeidi, also 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.

The ongoing violence in Baghdad has prompted U.S. commanders to reinforce troop strength in the city. Over the past weeks, a force expected to number nearly 12,000 has been assembling here to try to take the streets back from Sunni and Shiite extremists.

A U.S. statement Tuesday said about 6,000 additional Iraqi troops were being sent to the Baghdad area, along with 3,500 soldiers of 172nd Stryker Brigade Combat Team and 2,000 troops from the U.S. 1st Armored Division, which has served as a reserve force since November.

Much of the violence has been blamed on sectarian militias that have stepped up a campaign of tit-for-tat killings since the Feb. 22 bombing of a Shiite shrine in the northern city of Samarra.

Some of the reinforcements already have been seen patrolling a mostly Sunni neighborhood in western Baghdad, scene of armed confrontations between Sunni and Shiite gunmen.

Caldwell described the troops deployment as a gradual and continuous process, adding that the security plan needs Iraqi cooperation 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. Military force alone cannot achieve peace. It can only set the conditions to allow for peace to take hold and grow,” he said.

Many of the militias responsible for sectarian violence are linked to political parties that are part of Prime Minister Nouri al-Maliki’s national unity government, and they are reluctant to disband their armed wings unless others do the same.

The U.S. ambassador to Iraq, Zalmay Khalilzad, said talks were under way between various Sunni and Shiite groups to reach agreements and sign pledges to end sectarian fighting.

Also Wednesday, Romanian President Traian Basescu arrived in Baghdad to meet Iraqi and U.S. officials and visit some of the country’s 890 troops stationed there. Basescu was received by President Jalal Talabani and will meet other key U.S. and Iraqi officials.

In Baqouba, 35 miles northeast of Baghdad, four people were killed and 16 wounded in an explosion late Tuesday at a Shiite mosque, police said.

Police first said the blast was due to a U.S. airstrike, but the government agency that cares for Shiite shrines said later that “terrorists” had bombed the mosque, causing severe damage. The Shiite Endowment demanded that the authorities protect places of worship.