Kandahar, Afghanistan ? The blast came at night, as six foreigners with the French aid organization Action Against Hunger were settling down and preparing for bed. There was a bright flash, a loud explosion, and suddenly the windows were shattered, throwing glass far into the house.

As the group later learned, dynamite had been thrown over the back wall of the compound and had landed in the garden, just a few yards from the house. It was pure luck that everyone was away from the windows when it exploded.

“We were attacked, but we don’t know by who or why,” said Olivier Franchi, program coordinator for the group in Kandahar. “Was this a random attack, or was somebody sending us a warning message? We don’t know, but this is a very serious thing.”

Such attacks are becoming increasingly common in southern Afghanistan, particularly here in Kandahar, the birthplace of the Taliban. In the past several weeks, a car belonging to an aid group was riddled with 16 bullets; two foreign land-mine removal specialists were slightly injured when their car hit a booby-trapped mine; Afghan workers with aid groups have been tied up and robbed; a grenade was thrown at an Afghan relief organization’s car; and leaflets have been found urging locals to attack foreigners and Afghans who work with them.

“The level of violence here has increased in the past few weeks, there’s no doubt,” said Diane Johnson, head of the Kandahar office of Mercy Corps International, the aid group with the largest program in southern Afghanistan.

At a time when the United States and the international community are emphasizing the need to rebuild Afghanistan, many of the people working to accomplish that task say they are deeply worried about their programs and own safety.

The Afghan government of President Hamid Karzai and its supporters are especially eager to show that life can improve rapidly in the south, populated by the ethnic Pashtuns who formed the core of the Taliban Islamic movement, but that is where instability is greatest and aid programs most vulnerable.

In Kandahar, most relief groups have begun to draw down their staffs and develop contingency plans. Since almost all expect the violence to increase if the United States attacks Iraq, the talk is often of evacuation.

“We don’t want to leave like we are panicking, because that is exactly what these people want,” said Franchi, whose group was attacked on Jan. 29. “But we must also protect our staff. It is a very difficult situation.”

Most of the aid workers say they believe the attacks are linked to the recent increase in combat between Islamic militants and U.S. and Afghan troops in the area. There have been battles to the southeast near Spin Boldak and in the mountains to the north, and U.S. warplanes have pounded both areas, apparently spurring the militants to attempt retaliatory attacks.

In addition to soldiers and relief workers, Afghans have been targets. A land mine planted on a road near Kandahar blew up a minibus, killing at least eight people, and several provincial militia vehicles have been attacked and destroyed, killing several people.