U.S. troops opened fire near a checkpoint south of Baghdad (search) after their convoy was hit by a roadside bomb and a hospital official said Sunday at least eight people were killed in the second American attack in two days to have deadly results.

In other violence Sunday, a U.S. soldier assigned to Task Force Baghdad (search) was killed by a roadside bomb, while a Marine was killed in actir province.

Seven Ukrainian soldiers and one from Kazakhstan (search) also died in an apparently accidental explosion at an ammunition dump south of Baghdad.

U.S. officials said they had no information about the checkpoint shooting, which occurred overnight Saturday. Interior Ministry spokesman Col. Adnan Abdul-Rahman said a roadside bomb hit a U.S. convoy near a police checkpoint in Yussifiyah, nine miles south of Baghdad, and troops opened fire, killing two police officers and three civilians.

Dr. Anmar Abdul-Hadi of al-Yarmouk hospital said eight people died in the attack and 12 were wounded.

American commanders recently announced a change in response to roadside bombings. Rather than pushing on after the blast, they now stop and try to engage the perpetrators, who may have detonated the explosives remotely.

Hours before the attack, the United States acknowledged dropping a 500-pound bomb on the wrong house during a search for terror suspects outside the northern city of Mosul. The military said in a statement that five people were killed.

The house's owner, Ali Yousef, said 14 people died when the bomb hit at about 2 a.m. Saturday in Aitha, a town 30 miles south of Mosul. An Associated Press photographer at the scene said the dead included seven children and seven adults. The discrepancy between the death counts could not be reconciled.

Such attacks are exactly what the United States does not want prior to national elections scheduled for Jan. 30.

On Sunday, Secretary of State Colin Powell was asked on ABC's "This Week" how he would define success in Iraq's election, and he acknowledged concern about what will happen after the vote.

"Success is putting in place a government that is really elected and represents all of the people of Iraq ... and creating an Iraqi security force that is able to protect the country and protect the people of Iraq," he said.

A U.S. soldier assigned to the Task Force Baghdad was killed in a roadside bomb explosion, the military said without specifying where the attack occurred.

A Marine assigned to the 1st Marine Expeditionary Force also was killed in action Sunday while conducting security and stability operations in the western province of Anbar, which is home to the volatile city of Fallujah, according to a military statement released Monday. More details were not provided and identities were withheld pending notification of relatives.

At least 1,353 U.S. military members have died since the Iraq war began in March 2003, according to an Associated Press count.

Unknown assailants on Sunday shot Samarra's deputy police chief, Col. Mohammed Mudhafir, as he drove alone, Samarra police Maj. Raed Ahmed said.

Few details were known about the explosion that killed the Ukrainian and Kazakh soldiers. The U.S. military said late Sunday that the soldiers were cleaning up the ammunition dump.

Polish military spokesman Lt. Col. Artur Domanski said the explosion occurred at about noon, about six miles south of Suwaira. Eleven soldiers were wounded — seven Ukrainians and four Kazakhs, he said.

Ukraine's Defense Ministry said the soldiers were loading aviation bombs when one of the devices exploded.

Ukraine serves in a Polish-led contingent in south-central Iraq and is the fourth-largest contributor of troops to the war effort with 1,650 soldiers. Kazakhstan has sent a 27-strong contingent of military engineers and is the only Central Asian nation to contribute troops.

Nine Ukrainian soldiers have died in Iraq, including three in combat, and more than 20 have been wounded.

Elsewhere Sunday, Iraq's most influential Sunni group said it will abandon its call for a boycott of the elections if the United States gives a timetable for withdrawing multinational forces.

The Association of Muslim Scholars relayed its request to a senior U.S. embassy official at a meeting Saturday, a group spokesman said on condition of anonymity.

U.S. Embassy spokesman Bob Callahan on Saturday confirmed the meeting, which he described as an "exchange of views."

The first democratic vote in Iraq since the country was formed in 1932 is certain to see the Sunnis lose their dominance to the Shiites, who comprise 60 percent of Iraq's 26 million people. Sunni leaders have urged a postponement of the vote, largely because areas of Iraq where they dominate are too restive for preparations to begin.

In what appeared to be another effort to persuade Sunni Muslims to participate in the vote, interim Prime Minister Ayad Allawi met Saturday with 116 tribal leaders, clerics and political personalities from the restive provinces of Anbar, Salahuddine and Nineva, his office said Sunday.

The guests expressed support for "the democratic process in Iraq and cooperation with the government to stand against violence and terrorism," the office said.

In other developments Sunday:

— British Prime Minister Tony Blair said Britain and the United States will send a team to Iraq to reassess security in the face of spiraling violence. "In the key area around Baghdad there is no doubt about it at all. We have got to deal these people a blow," Blair told British Broadcasting Corp. TV.

— U.S. forces released about 230 Iraqis who had been detained in Abu Ghraib prison, according to a military statement.