In Iraq, a top police chief was killed in the northern city of Mosul Thursday after a suicide bomber struck officials touring the site of a previous blast. Two other police officers were killed and one U.S. and one Iraqi soldier were wounded.  The attack happened at the site of Wednesday's explosion that killed 34 people and wounded more than 200. VOA's Deborah Block has more from Baghdad.

The violence began as gunmen ambushed officials who were touring Wednesday's blast site in Mosul, the capital of Ninevah province.  The gunmen opened fire on the group, including Ninevah province police director General Saleh Mohammed Hassan, as they walked through the wreckage.  The officials fled and, according to a police spokesman, a suicide bomber wearing an explosives vest under an Iraqi police uniform moved toward Hassan's car and detonated his explosives, wounding the police chief.   Hassan was taken to an Iraqi army hospital where he was pronounced dead.  

Wednesday's explosion, at the same site, destroyed a vacant apartment building and adjacent homes, shortly before Iraqi troops came to investigate tips about a weapons cache.  A Mosul local talks about the destruction.

He says our houses collapsed and an alley way was completely destroyed.

In the Iraqi capital, Baghdad, a roadside bomb struck a police car on patrol, killing two officers. The explosion happened in the predominately Shi'ite neighborhood of Karradah in central Baghdad.   Mahdi Mousa saw what happened.

He says the bomb exploded in the morning, wounding two policemen and several civilians.  He adds that one of the wounded had serious leg injuries.

American and Iraqi forces have made significant gains in chasing insurgents from Baghdad.  But the U.S. military says some insurgents have fled north into cities like Mosul where violence has intensified.