BAGHDAD — The American command announced yesterday the deaths of 14 more American troops, most killed in powerful roadside bombs in Baghdad. Thick, black smoke rose from the heavily fortified Green Zone after a mortar barrage as insurgents struck back despite a massive military offensive.

But as always, attacks claimed far more Iraqi lives.

A suicide truck bombing outside the Sulaiman Bek city hall in a predominantly Sunni area of northern Iraq killed at least 17 people, including the mayor, and wounded 66, officials said. Blame fell on Al Qaeda, which has targeted government officials it accuses of collaborating with American forces and the Iraqi government by participating in the political process.

“The enemy ‘s going to push back, he’s going to try and make us look unsuccessful,” a military spokesman, Lieutenant Colonel Christopher Garver, said. “We have said it’s going to be a long, tough fight over the summer, this is part of that long, tough fight.”

At least 15 servicemen have been killed since Tuesday, including 12 in a series of attacks beginning Wednesday. The military had previously announced one of the deaths.

The deadliest attack was a roadside bomb that struck a convoy in northeastern Baghdad yesterday, killing five American soldiers, three Iraqi civilians, and one Iraqi interpreter, the military said. About 12:30 p.m. the same day, a rocket-propelled grenade struck a vehicle in northern Baghdad, killing one soldier and wounding three others.

The American military has sought to seize the momentum against Al Qaeda and other militants with the arrival in Iraq of some 30,000 additional troops. It has launched several large-scale operations.

But the military has also faced a series of recent attacks on American soldiers, who are more vulnerable as they increasingly take to the streets and remote outposts, and the bombs appear to be growing more powerful. Some American soldiers have reported a recent increase in the use of rocket-propelled grenades.

Colonel Garver said one of the aims of the latest offensives was to deprive militants of their safe havens where they have been able to assemble huge quantities of explosives.

The latest U.S. deaths raised to at least 3,545 the number of American troops who have died since the war began in 2003, according to an Associated Press count. Some estimates put the number of Iraqi civilian deaths in the hundreds of thousands.