Baghdad, Iraq ? Gunmen in police uniforms staged a brazen daylight raid on bus stations in central Baghdad on Monday, kidnapping at least 50 people, including travelers, merchants and vendors selling tea and sandwiches.

The operation was a direct challenge to Prime Minister Nouri al-Maliki’s efforts to restore security in the capital, which has been hard hit by suicide attacks, roadside bombs and sectarian death squads.

Gunmen arrived at midmorning Monday and began randomly grabbing people in the shabby business district, where several transportation companies are based and buses pick up passengers bound mostly for Jordan, Syria and Lebanon, Lt. Col. Falah al-Mohamedawi said. Both Shiites and Sunnis work in the area.

The attackers blocked the roads and beat people before putting bags on the captives’ heads and leading them to vehicles one-by-one, a witness told an Iraqi television station. They herded their victims into more than a dozen vehicles, according to witnesses and officials.

“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 taken away, along with merchants, passers-by and even men selling tea and sandwiches.

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.

Monday’s kidnapping was the latest in a series of setbacks for al-Maliki. The Shiite prime minister has also been frustrated in his efforts to crack down 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 al-Maliki 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 “they should be national independent figures.” Lawmaker Hameed Majid Mosa called on al-Maliki to use his constitutional authority to fill the posts.

The 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.

The Bush administration hopes a unity government will drain support for the Sunni-led insurgency and restore order in Baghdad and elsewhere in the country, enabling the United States to begin withdrawing its forces.