Gunmen in police uniforms staged a brazen daylight raid on bus stations in central Baghdad on Monday, kidnapping at least 50 people, including would-be travelers, merchants and vendors selling tea and sandwiches. The operation was a direct challenge to the prime minister's efforts to restore security in the capital.

The victims were herded into more than a dozen vehicles, according to witnesses and officials. It was not known who was behind the attack, but the Interior Ministry denied that police were involved.

The attackers arrived at mid-morning and began randomly grabbing people in the shabby business district, where several transportation companies are based and buses pick up passengers traveling mostly to Jordan, Syria and Lebanon, Lt. Col. Falah al-Mohamedawi said.

CountryWatch: Iraq

"They took all the workers from the companies and nearby shops," said Haidar Mohammed Eleibi, who works for the Swan Transportation Co. in the Salihiya area.

He said his brother and a cousin were among those detained, along with merchants, passers-by and even men selling tea and sandwiches.

"They did not give any reason for it," he said. "Police came afterward and did nothing."

The Shiite-dominated Interior Ministry, which oversees the police and has been accused of backing militias in sectarian violence, denied its forces were behind the attack.

Another transportation worker Amjad Hameed said 15 cars belonging to police rushed into the area and began randomly seizing people. "We asked them why but nobody replied," he said, adding that Iraqi forces and Americans came to the site afterward. The U.S. military said it had no information about the event.

Another witness told an Iraqi television station that the gunmen blocked the roads and beat people before putting bags on the captives' heads and leading them one-by-one to the vehicles.

In a similar attack on a locally owned security firm March 8, gunmen dressed as Interior Ministry commandos stormed into the al-Rawafid Security Co.'s east Baghdad headquarters and took away 50 people, many of them former military personnel from Saddam Hussein's regime. Those employees have not been heard from since.

It was the latest in a series of setbacks for Prime Minister Nouri al-Maliki, who announced a security plan late last month aimed at restoring order in Baghdad, which has been hit hardest by suicide attacks, roadside bombs and sectarian death squads.

He has not released details of the plan, and violence has persisted in the capital of 5 million people, where at least eight people were killed Monday, including a Shiite school guard and two Sunni brothers who were shot to death as they were driving to college.

Iraqi police also found the blindfolded and bound body of a man who had been shot in the head and chest and another body that had been shot in the head in separate locations in Baghdad.

Eight other deaths were reported nationwide on Monday, a day after masked gunmen stopped two minivans carrying students north of Baghdad, ordered the passengers off, separated Shiites from Sunni Arabs, and killed the 21 Shiites "in the name of Islam," a witness said.

Al-Maliki also has been frustrated in his efforts to crackdown on sectarian and militia violence in the oil-rich southern city of Basra, where attacks have been unabated despite his declaration of a state of emergency on Wednesday.

And the Shiite prime minister still has not been able to reach consensus among Iraq's ethnic and sectarian parties on candidates for interior and defense minister — posts he must fill to implement his ambitious plan to take control of Iraq's security from U.S.-led forces within 18 months.

Former Prime Minister Ayad Allawi's secular Iraqi List party criticized the latest delay in announcing the new ministers, insisting that "they should be national independent figures" and calling on al-Maliki to use his constitutional authority to fill the posts.

The U.S. State Department also stressed the importance of filling the positions to complete al-Maliki's government of national unity, which took office just over two weeks ago.

"I know that there are very active discussions under way right now to fill those positions. We think that that is important. We hope that that, in fact, occurs in the very near future," State Department spokesman Sean McCormack said.

"That will send an important signal to the Iraqi people that they have a full government working on their behalf, especially in those positions where you would have individuals that would be free from the taint of association with militias," he added.

Elsewhere, U.S.-led forces fired artillery at the train station in the western city of Ramadi, in the volatile Anbar province, "targeting four military-aged males unloading a weapons cache," according to the U.S.-Iraqi Joint Operations Center.

A hospital official, Dr. Omar al-Duleimi, said five civilians were killed and 15 wounded by American forces in Ramadi, 70 miles west of Baghdad.

The Joint Operations Center said the mission had "positive effects on the target," but it denied the report that civilians were killed or injured.

The influential Sunni Association of Muslim Scholars, meanwhile, warned the U.S.-backed Iraqi government against participating in any assaults against Anbar, a vast province that stretches from western Baghdad to the borders with Syria and Jordan.

"Its consequences would be very dangerous for the Iraqi society and for the government," said Mohammed Bashar al-Faidi, a spokesman for the Sunni group believed to have links to insurgents, said at a news conference.

Al-Maliki has said that his government was working on a plan to restore security to the provincial capital of Ramadi and that Iraqi forces would work with U.S. troops, and about 1,500 U.S. combat troops have been moved from Kuwait to the province.

Separately, a 30-year-old Iraqi man accused of helping the kidnappers of British aid worker Margaret Hassan also was sentenced to life in prison on Monday, while two other suspects were acquitted, a court official said.

Hassan, 59, the director of CARE international in Iraq and a citizen of Britain, Ireland and Iraq was abducted in Baghdad in October 2004. She was killed a month later and her body has never been found.

In other violence Monday, according to police:

— Gunmen in two cars killed a member of the Badr Brigade, the armed wing of the Supreme Council for the Islamic Revolution in Iraq, near his home in western Baghdad.

— The head of the Abu Ghraib city council and his driver were killed in a drive by-shooting west of Baghdad.

— Gunmen in two cars killed a local councilman and one of his guards as they were driving in Baghdad's upscale al-Mansour neighborhood.

— Gunmen also raided a printing press in the downtown Baghdad neighborhood of Karradah on Monday, abducting the owner.

— Police found the bodies of four men in the Tigris River in Suwayrah, 25 miles south of Baghdad.

— Gunmen killed a former member of the local Baath Party and the brother of an interpreter working for British troops in Amarah, 180 miles southeast of Baghdad. Police said the gunmen may have mistaken the victim for his brother.