BAGHDAD Missiles and mortars struck areas of Baghdad and central Iraq on Saturday where violence and civilian deaths had decreased in recent weeks, raising concerns that insurgents were adapting their strategy to get around an increase in U.S. troops.

At least 30 Iraqis were killed nationwide, including seven in a mortar barrage aimed at a Shiite residential area north of Baghdad in the town of Khalis. Car bombs killed four people in Kirkuk, where a police officer was shot to death earlier in the day, and two were killed in a missile attack on a farming village near Ramadi.

The Ramadi attack unleashed panic in an area that had been relatively peaceful in recent weeks, said Juma Salim, a 62-year-old farmer who claimed that the presence of U.S. troops provoked the violence.

Kirkuk has suffered a rash of attacks since insurgents began fleeing the U.S.-led crackdown in Baghdad. Gunmen there killed an Iraqi police lieutenant, and three apparently coordinated car bombs killed four shoppers in a marketplace, including a 4-year-old. Forty-six people were injured.

The attacks spurred further sweeps against suspected insurgent hide-outs in which U.S.-led troops killed two and detained 16, said Lt. Col. Christopher Garver, spokesman for multinational forces in Iraq.

American officials say they have captured dozens of key insurgents and disrupted their operations in campaigns launched in the last two months as the increase in U.S. troops has allowed more concerted moves against hot spots such as Baghdad and the so-called Sunni Triangle to the west and south.

But as violence in those areas has eased, car bombs and small-arms fire increasingly have been directed against Iraqis in more distant areas. On Thursday, synchronized truck bombings in three far northern villages killed as many as 400 people of the minority Yazidi sect in the deadliest attack on civilians in the Iraq conflict.

Iraq’s Sunni vice president, Tariq al-Hashemi, promised better treatment and a review for the inmates crowding the country’s prison system in a video released Saturday showing a boisterous welcome from prisoners jammed inside tarp-covered cages.

Rights groups have complained about random detentions and overcrowding in Iraq’s prisons. Most of the inmates are believed to be Sunnis accused of participating in the insurgency, but critics say many are innocent and have been held for long periods without charge.