BAGHDAD – Violence killed at least 42 people yesterday, including 16 bus passengers caught in a roadside bombing in southern Iraq, after the deadliest day for U.S. troops in precisely six months.

The U.S. military announced that three American soldiers were killed in a roadside bombing north of Baghdad on Monday, bringing to eight the number of troops who died that day. The last time so many U.S. military personnel were killed in Iraq was Sept. 10, when 10 died.

Bloodshed has increased recently, despite what the military said has been a 60 percent drop in attacks across Iraq since June. Last Thursday, two massive bombs killed 68 people in Baghdad’s Karradah neighborhood. On March 3, two car bombings killed 24 people in the capital.

According to an Associated Press count, at the height of unrest from November 2006 to August 2007, on average approximately 65 Iraqis died each day as a result of violence. As conditions improved, the daily death toll steadily declined. It reached its lowest point in more than two years on January 2008, when on average 20 Iraqis died each day.

Those numbers have since jumped. In February, approximately 26 Iraqis died each day as a result of violence, and so far in March, that number is up to 39 daily. These figures reflect the months in which people were found, and not necessarily – in the case of mass graves – the months in which they were killed.

Military spokesman Rear Adm. Gregory Smith said Sunday that recent violence should not be taken as evidence of “an increase or a trend of an increase.”

“I think we need to continue to look at historically what has happened over the last year to really put in perspective a one-week or two-weeks’ worth of activity inside Baghdad,” Smith said.

But Smith, in what has become a military mantra of caution, also noted that “on any given day, al-Qaida and other extremist groups are still very much disposed toward handing out violence indiscriminately to achieve whatever means and ends they hope to achieve with those attacks.”

While al-Qaida in Iraq is Sunni, Shiite extremists with alleged ties to Iran are also believed to have carried out attacks.

In an interview with CNN yesterday, Gen. David Petraeus, the top U.S. commander in Iraq, said he was in favor of substantive discussions with Iran about what the U.S. claims is Tehran’s continued funding and training of extremists in Iraq.

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 U.S. 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 U.S. 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.

Yesterday’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 U.S. 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.