BAGHDAD - A truck packed with rockets blew up yesterday in a Shiite area of Baghdad, killing 18 people in the deadliest single blast in the city in more than three months. Three U.S. soldiers were killed by gunfire in Hawijah, north of the capital.

A U.S. military spokesman said the blast appeared to have been an accident that occurred as Shiite militiamen were transporting the weapons through a densely populated neighborhood of northern Baghdad - possibly to fire at a nearby American base.

Iraqi police said a suicide truck bomber had targeted the house of an Iraqi police general, who was not at home but whose nephew was among those killed. U.S. officials said 75 people had been wounded, and police said they included the general's elderly parents.

But the U.S. military disputed the police account, saying Shiite extremists were transporting rockets and mortars on a tractor-trailer when the weapons mistakenly exploded. Witnesses also confirmed the vehicle was carrying weapons.

"They were trying to attack us . . . and it went off [accidentally]" said U.S. military spokesman Lt. Col. Steve Stover, who provided the death toll. "They wouldn't waste rockets like that" on a suicide attack.

The force of the blast crumbled several two-story buildings, buried cars under rubble, sheared off a corrugated steel roof and left a large crater on the residential street.

Yesterday's carnage was a grim reminder of the bombs and killings that rocked the capital before President Bush rushed about 30,000 reinforcements to Iraq last year to curb a wave of Shiite-Sunni slaughter.

More recently, violence has dropped sharply since a May 11 cease-fire ended seven weeks of fighting between U.S. and Iraqi soldiers and Shiite militia in the capital's Sadr City district.

Nevertheless, a car bomb exploded last night in the Shiite district in east Baghdad, killing seven people. *