Story Highlights• New Baghdad suicide blast kills at least 12
• U.S. Defense Secretary Robert Gates arrives in Iraq
• Commander arrested after Wednesday attacks kill 198, wound about 240
• Video claims to show executions of 20 Iraqi security forces
Adjust font size:
BAGHDAD, Iraq (CNN) -- U.S. Defense Secretary Robert Gates arrived in Iraq on Thursday after a bloody 24-hour stretch in Baghdad that left more than 200 people dead.
Gates -- who intends to meet with U.S. commanders and Iraqi government officials -- has been visiting other countries in the region and his stop in Iraq is an unannounced visit, a pool report said.
He is coming to the country as bombing assaults across the capital on Wednesday and Thursday claimed scores of victims.
At least 198 people were killed in six bombings on Wednesday and 12 more were killed in a blast on Thursday.
The carnage prompted outrage worldwide and concern among U.S. and Iraqi troops trying to establish peace in Baghdad with its two-month old crackdown called Operation Enforcing the Law.
Ashraf Qazi, the U.N. special representative in Iraq, Thursday denounced the "killing and wounding more than 500 innocent civilians, including men, women and children," saying the attacks were "malicious and premeditated mass murders, aimed at tearing apart prospects for peaceful and lasting coexistence among Iraq's different communities."
He urged all Iraqis "to resist being pushed into the abyss of calamitous sectarianism" and "called on Iraqi authorities to vigorously pursue the criminal perpetrators of these atrocious acts and bring them to justice."
Many of those killed on Wednesday died in a blast at the Sadriya market, one of the capital's oldest and busiest venues. The Interior Ministry said 140 were killed and 150 were wounded in that incident.
It was the worst bombing in the Iraqi capital since the 4-year-old war began, topping the February toll of 130 dead in a bombing in the same marketplace.
Prime Minister Nuri al-Maliki's office later said a brigade commander was arrested because of "the weakness of security measures put in place to protect civilians in Sadriya."
The arrested officer, whose name was not immediately released, was the Iraqi Army commander in charge of security in Sadriya, and will face an investigative committee looking into the bombings.
Gates made remarks about Iraq while he was visiting the Egyptian capital of Cairo on Wednesday and stressed the need for political reconciliation.
"I think that there is progress being made. I believe that faster progress can be made in the political reconciliation process in Iraq," Gates said.
He said there could be progress once "sectarian" factions "decide to live peacefully with one another."
Gates explained that there aren't "thousands of people in the streets in Iraq trying to kill each other."
Video purports to show 20 executions
An insurgent group that said it executed 20 Iraqi security force members posted a video Thursday of the killings on the Web, with the voice of the late al Qaeda in Iraq leader Abu Musab al-Zarqawi apparently speaking in backdrop of the video as the men were methodically slain.
The men, bound and blindfolded, were lined up crouched on their knees in a field. A masked gunman shot each one of them in the back of the head. The video showed two other masked gunmen nearby and a photographer, who followed the gunman as he walked along and shot the people.
They were killed with what is believed to be al-Zarqawi's voice in the backdrop, saying "decide which side you want to be on." Words across the screen said it was al-Zarqawi's voice.
Al-Zarqawi was killed in a U.S. air raid last year in the Diyala province town of Hibhib.
The Islamic State of Iraq -- an umbrella group of Sunni extremists that includes al Qaeda in Iraq -- said Tuesday it killed the security officers after several demands it made of the Iraqi government hadn't been met.
CNN cannot verify the authenticity of the video, found on Islamist Web sites, and the claims that were made on it.
3 U.S. soldiers killed
Three U.S. soldiers were killed in the Baghdad area Wednesday, the U.S. military said Thursday.
Two died and another was wounded when their vehicle was hit by a roadside bomb. Another soldier was killed "when a combat security patrol was attacked with small arms fire." the U.S. military said.
The U.S. military death toll in the Iraq war now stands at 3,315, including seven civilian employees of the Defense Department.
CNN's Jomana Karadsheh contributed to this report.