Petraeus said he did not meet with Iranian President Mahmoud Ahmadinejad during his visit to Iraq last week because he thought it would have been a "relatively meaningless encounter".

But he added: "What we would like to do with Iran of course is sit down across the table and let's discuss. You know, the Iranians have pledged at the very highest levels to stop arming, training, funding and equipping and directing the special groups and these other militia extremist elements ... and yet it appears very clear that Iran does continue."

The roadside bombing that killed the three US soldiers and an interpreter Monday took place in Diyala, a violent province where al-Qaida in Iraq has been active. Another soldier was wounded.

The five other US soldiers were killed while on foot patrol in central Baghdad. A suicide bomber approached them and detonated his explosives vest. Three American troops and an Iraqi interpreter were wounded. Iraqi police said two civilians also were killed in the attack.

Tuesday's attack on the bus traveling from Najaf to Basra killed 16 civilians and wounded 22, a policeman said.

Gunmen also sprayed another bus with machine-gun fire shortly after it hit a roadside bomb in eastern Baghdad. One person was killed and four others were wounded, police said. The bomb was apparently targeting a nearby police patrol.

In Duluiyah, 45 miles north of Baghdad, police said a suicide bomber blew up his truck at a checkpoint near the headquarters of the local Awakening Council, killing five people. Awakening Councils are made up of mostly Sunni fighters who have accepted US backing to switch allegiances and fight al-Qaida in Iraq.

And in Kut, 100 miles southeast of Baghdad, clashes with Shiite cleric Muqtada al-Sadr's Mahdi Army militia left 12 dead and 14 injured. Thirty people were arrested. Southern Iraq often sees clashes between rival Shiite groups battling for power.

In Mosul, an unknown number of gunmen attacked a police checkpoint in Mosul, killing four policemen and injuring one civilian. Four of the attacking gunmen also were killed in the firefight, according to a Ninevah police officer who spoke on condition of anonymity.

(Xinhua News Agency March 12, 2008)