BAGHDAD, Iraq — Attacks against U.S. troops have increased following a call earlier this month from al-Qaida in Iraq's leader to target American forces, the top U.S. military spokesman said today.

Maj. Gen. William B. Caldwell also said that Iraqi and American troops were expecting violence to increase further during the Islamic holy month of Ramadan, which begins next week.

The attacks against U.S. troops were mostly carried out by suicide car bombers or roadside bombs. He added that the number of killings by death squads also had increased in the past week.

The rise in attacks against American forces came after a threat issued Sept. 7 by Abu Ayyoub al-Masri, also known as Abu Hamza al-Muhajer.

The military said an American soldier was killed by a roadside blast northeast of Baghdad on Tuesday.

The news came after the U.S. military announced the deaths of four other soldiers in Iraq. One was killed Tuesday by a suicide car bombing, which also wounded two other soldiers. Another two soldiers were killed Sunday — one by small arms fire and the other by a roadside bomb in Baghdad. A fourth soldier, assigned to a medical task force, died Monday of non-combat related injuries in the capital.

In other violence, an Iraqi police headquarters in Baghdad was hit by a suicide truck bomb, killing at least seven people in a deadly 24-hour period that saw more than 45 killings throughout Iraq, authorities said.

The truck bomb attack in the southern Baghdad neighborhood of Dora happened as policemen were coming on duty, said Capt. Jamil Hussein. At least 14 others were injured, and he said the number of casualties was expected to rise.

Police in Mosul confirmed that tandem bombings killed 21 people near the northern city and wounded 50 others.

A parked car bomb detonated near an Iraqi army base in Sharqat, about 45 miles south of Mosul, on Tuesday night, and a suicide bomber detonated his explosives as a crowd gathered at the scene of the first bombing, police said.

Another policeman was killed when a mortar round landed near a patrol in northern Baghdad, police Lt. Bilal Majid said. Two civilians were also wounded in the attack in the Waziriya neighborhood, Majid said.

Also today, the mutilated body of a policeman was turned in to the morgue in Kut, about 100 miles southeast of Baghdad, after being found in the al-Falahiya district east of the city in the morning.

The body of Mahmoud Hassan Mohammed was found blindfolded with his arms and legs cuffed, and he was shot in various place and showed signs of torture, morgue official Mamoun Ajeel Al-Rubai'ey said.

The body of an unknown civilian in a similar condition also was turned in to the morgue after being dragged out of the Tigris River, Al-Rubai'ey said.

Nearly 200 bodies of Iraqis who had been tortured and shot have turned up around Baghdad in the past week.