Gunmen in military uniforms kidnapped shopkeepers and bystanders Thursday from a major commercial area in Baghdad, the second mass abduction in the capital in a month, and nearly 30 people were killed or found dead elsewhere in Iraq.

The attackers drove up to the busy Sanak area in about 10 sport utility vehicles and began rounding up people from the stores and the streets.

Reports on the number of victims varied, with police officers and witnesses saying 50 to 70 people were abducted. The interior ministry later said that up to 29 people who had been abducted had been released.

Elsewhere in Baghdad, a suicide car bomber slammed into an Iraqi army check point, killing a soldier and a civilian and wounding nine other people, police said.

Police in the mostly Shiite Wasit province southeast of Baghdad also found 17 bullet-riddled bodies — bound, blindfolded and bearing signs of torture — including five that were dumped in a flour mill in the town of Wahda.

Click here to go to FOXNews.com's Iraq Center.

Three other bodies, including one that was beheaded, were found elsewhere in a volatile area southwest of the capital.

The violence underscores the difficulties the Iraqi government faces after it unveiled a plan to assume responsibility for security in Baghdad, allowing U.S. forces to move to the periphery of the capital, by early next year.

Sen. John McCain, R-Ariz., said the United States should to deploy 15,000 to 30,000 more troops to control the sectarian violence and give moderates within the democratically elected government the stability they need to move Iraq in the right direction.

"The American people are disappointed and frustrated with the Iraq war, but they want us to succeed if there's any way to do that," McCain, a 2008 presidential hopeful, said at a news conference with the other legislators at the U.S. Embassy in Baghdad's heavily fortified Green Zone.

Lt. Gen. Raymond Odierno, meanwhile, took over the command of the Multi-National Corps-Iraq from Lt. Gen. Peter Chiarelli. The new No. 2 general in Iraq said the main challenges in Baghdad were sectarian violence and car bombs, and he stressed the effort to end the attacks needs to be multipronged.

"This is not just a military solution," he told reporters after an outdoor handover ceremony in front of one of Saddam Hussein's former palaces at Camp Victory. "It's a combination of diplomatic, economic and military programs that have to move forward in Baghdad."

The Sanak area — one of the capital's main commercial districts — holds stores selling auto parts, agricultural equipment and the small power generators that are ubiquitous in Baghdad due to severe power shortages.

The stores are owned by a mix of Shiites, Sunnis and others, and it was not immediately clear why the area was targeted. But suspicion fell on militias, which are believed to have infiltrated police forces and have killed hundreds in sectarian violence, personal vendettas and kidnappings for ransom.

On Nov. 14, suspected Shiite militiamen in Interior Ministry commando uniforms abducted scores of men from an office that handles academic grants and exchanges for the Higher Education, which is predominantly Sunni Arab. Several of those kidnap victims apparently were later released, although there were conflicting accounts about how many people were involved.

Many victims of other past kidnappings have been found among the dozens of bullet-riddled bodies that turn up daily on the streets of Baghdad.

Mohammed Qassim Jassim, a 37-year-old owner of a clothing store in the area, said the attack started about 11 a.m.

"We heard cars and shootings in the area and then we saw gunmen wearing Iraqi army uniforms and driving SUVs who were snatching people from the shops and street. It took like 20 minutes for them to fan out and control the area," Jassim said.

Iraqi security forces sealed off the area and were interviewing witnesses, while panicked store owners closed their shops and fled.

A spokesman for the Defense Ministry, which oversees the army, stressed the difficulties in controlling the distribution of uniforms.

"Anyone can buy military or police uniforms from the market, although we have issued orders to confiscate these uniforms and punish the owners," spokesman Mohammed al-Askari said.

Video from AP Television News showed boarded and locked store fronts with the blue dome of a Shiite mosque in the background. Few people were on the street of what is usually a bustling area.

Officers were on high alert, stepping up security after receiving tips that militants were moving car bombs into the Shiite Sadr City slum.

A car bomb killed two policemen who were trying to defuse it and wounded four civilians late Wednesday in the sprawling district, police Capt. Mohammed Ismail said. He said explosives experts successfully defused a second car bomb in the same area.

The capital has seen a series of attacks since a Feb. 22 bombing of a Shiite shrine in Samarra set off a cycle of retaliatory violence between the majority sect and disaffected Sunnis, who were dominant under Saddam Hussein but lost power with his ouster.

In other violence reported by police Thursday:

— Gunmen stormed a boys' school in southwestern Baghdad, killing a Shiite guard.

— Gunmen killed two people in separate attacks northeast of the capital and a police officer was shot to death in the northern city of Mosul.

— A roadside bomb targeting an Iraqi army patrol exploded in Musayyib, 40 miles south of Baghdad, killing one soldier.

— A roadside bomb stuck a joint patrol of police and Interior commandos, killing two commandos and wounding one policeman in Samarra, 60 miles north of Baghdad.

Click here to go to FOXNews.com's Iraq Center.