A bomb explosion on a bus in southern Afghanistan has killed at least 16 people and injured several others.

This is the second attack within a week in the southern Afghan province of Helmand. Local security officials say the bomb exploded on a small bus about 15 kilometers west of the provincial capital, Lashkargah. Almost half the victims are said to be children.

No one has claimed responsibility for the attack, but provincial authorities are blaming members of the ousted Taleban government.

In an attack last Thursday in another district of Helmand Province, suspected Taleban fighters killed six Afghan soldiers and a worker for a U.S. aid organization. The troubled province was a stronghold of the hard-line Islamic government known as the Taleban, until a U.S.-led invasion removed it from power in late 2001.

Fugitive Taleban fighters and their allies have waged a low-level guerrilla war in Afghanistan since then. They have regularly targeted Afghan and coalition forces as well as members of western aid organizations. The violence has claimed dozens of lives this year.

Meanwhile, officials in Kabul said that two supporters of the al-Qaida terror network were killed when a bomb they were making went off in the western part of the capital.

The United Nations and aid groups have repeatedly warned that security conditions are deteriorating in the country. Following an attack on U.N. workers last week, the United Nations suspended travel for its staff in the Helmand region.

The aid workers and the United Nations have urged the international community to expand the area of responsibility of international peacekeeping forces, which are providing security in the Afghan capital.

NATO officially took command last week of that peacekeeping force, the International Security Assistance Force, but NATO officials have given no indication they are considering expanding the security net outside of Kabul.