KABUL, Afghanistan - A crowded Afghan passenger bus struck a roadside bomb yesterday in the violent southern province of Kandahar, killing 30 people and injuring more than three dozen others, Afghan officials said. As many as 10 children were reported to be among the dead.

The incident underscored the growing danger of road travel in much of Afghanistan, even on main highways, and the peril faced by civilians engaged in such mundane activities as walking to school, going to the market, or riding a bus.

The United Nations reported last week that August had been the deadliest month this year for civilians, who often find themselves caught in fighting between Western troops and insurgents. At least 1,500 noncombatants have been killed this year, the report said.

Roadside bombs are almost always meant for foreign troops. The crude but powerful devices claim far more Western troop casualties than out-and-out clashes with the Taliban and other militants. But they are indiscriminate killers: Civilians also use the roads traveled by military convoys.

At the time of yesterday’s blast, a contingent of soldiers had blocked off the main route to sweep it for explosives. The bus turned onto a parallel dirt road and struck a buried bomb there.

Intercity buses are the main mode of transport for Afghan workers and families, few of whom can afford to fly across the country’s vast distances. The bus was traversing a popular route from the western city of Herat to Kandahar, the hub of southern Afghanistan.

The explosion, which left the bus charred and twisted, took place in the district of Maiwand, on Kandahar city’s western fringes. The area has long been a battlefield between Western troops and Taliban fighters. US troops have begun to take a greater combat role in Kandahar province, where until recently Canadians made up the bulk of foreign forces in insurgent-plagued districts.

The Afghan Interior Ministry put the number of deaths from the blast at 30 and the injured at 39, although some local and provincial officials provided different figures.

Civilian deaths, either by foreign forces or the Taliban, have caused many Afghans to question the price of the fight against the insurgents, now entering its ninth year. The Obama administration is still struggling to come up with a coherent war strategy, even as some NATO allies question whether the conflict is winnable.

Yesterday, Obama opened a new round of meetings to rethink his strategy in Afghanistan as he weighs a request for more troops from General Stanley McChrystal, the top US commander on the ground.

Obama hosted the new NATO secretary general, Anders Fogh Rasmussen, who said he agreed with the president that it was more important to figure out first what the mission should be in Afghanistan. “I agree with President Obama in his approach - strategy first, then resources,’’ Rasmussen said, sitting next to Obama in the Oval Office.

Today, Obama plans a meeting on Afghanistan with his entire national security team - including McChrystal and top military and diplomatic officials - in the White House situation room.

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