KABUL, Afghanistan -- A powerful truck bomb yesterday killed at least 25 people, more than half of them children, in an eastern province near Kabul. Authorities speculated that the explosives-laden vehicle was intended for an attack in Kabul.

Three U.S. soldiers also were killed by roadside bombs, the U.S. military said, two in southern Afghanistan and one in the east. The incidents followed a pattern of escalating violence in widely scattered areas of Afghanistan.

The truck blast happened in Lowgar province. The vehicle, traveling on Afghanistan's main north-south highway, apparently ran off the road and overturned before dawn. When police and civilians approached and tried to right the truck, it blew up, the Interior Ministry said.

Most of the dead were civilians, including at least 13 students from a nearby primary school, local officials said. The thunderous blast left a huge crater in the highway, hurled debris over a wide area and collapsed several nearby shops and homes.

The truck was piled high with a load of timber, with the payload of explosives buried underneath, police said. Officials were trying to determine if it was triggered remotely when police and other help arrived, or if it detonated when the truck was moved.

Lowgar Police Chief Ghulam Mustafa said the truck's driver had disappeared, and officials were looking into the possibility that the Taliban had been transporting the explosives to the capital, which has been relatively calm lately. But an explosion of this size and strength in a crowded area such as Kabul likely would have caused many more deaths and injuries.

Meanwhile, officials said Afghanistan's government has revised a law that stirred an international outcry because it essentially legalized marital rape. The new version no longer requires a woman submit to sex with her husband, only that she do certain housework.

Over the past year, Lowgar province gradually has become a hotbed of insurgent activity, alarming Western military officials and fostering the impression that the Taliban were tightening a noose around Kabul. Travelers on the main road south from the capital face the threat of ambush, abduction or banditry when passing through the province.

In an effort to weaken militants' grip on the area, U.S. troops from the 10th Mountain Division, based in Fort Drum, N.Y., have been deployed in Lowgar and adjoining Wardak province for about six months. In addition, a "village guards" initiative has been set up in the two provinces, which Afghan and Western authorities say eventually may be expanded countrywide. Locals work as a kind of auxiliary police force to try to keep insurgents from overrunning villages.

The latest bloodshed coincided with a U.S. military offensive in southern Afghanistan's Helmand province, a center of both the insurgency and the drug trade. In the last week, about 4,000 U.S. Marines have secured the lower Helmand River Valley, and commanders say they plan to hold the territory with a string of new outposts and a concerted effort to reach out to mistrustful tribal elders and village leaders.