KANDAHAR, Afghanistan — A roadside bomb hit a Afghanistan's main city on Tuesday, killing four Nepalese guards and an Afghan driver, official said.

The incident -- the first deadly attack on the world body in Afghanistan for 11 months -- came after an assault on a Danish aid group and a report accusing militants of targeting civilians for Iraq-style violence.

Tuesday's victims were traveling in a UN convoy of at least three vehicles through Kandahar city, when the blast hit their gray sports-utility vehicle, according to Esmatullah Alizai, Kandahar's provincial police chief, and witnesses.

Four Nepalese men working as UN security guards as well as their Afghan driver were killed in the blast, Alizai said.

An Associated Press reporter saw the charred bodies of two of the victims lying on the road close to the damaged vehicle, as police tried to secure the scene. The blast detached two doors from the car and flung them 50 yards onto the other side of a canal and gouged a crater in the road.

The UN confirmed that four Nepalese contractors and an Afghan driver working for the United Nations Office for Projects Services died in the attack.

"Intentional attacks on civilians are a clear violation of international humanitarian law and the UN will be pursuing full accountability for those who are behind this," the UN said in a statement released in the capital, Kabul.

There was no immediate claim of responsibility.

However, the attack underlines concern that Taliban-led insurgents are operating even in the closely guarded southern capital, despite the stationing of thousands of foreign troops in the region.

NATO-led forces are currently focused on clearing neighboring Helmand province, the world's biggest producer of opium, of Taliban fighters in order to allow the renovation of a hydroelectric power plant.

Fixing the Kajaki dam is a flagship development project supposed to persuade Afghans to side with the feeble government of President Hamid Karzai. However, much of the country remains dangerous for aid workers.

In eastern Laghman province, militants armed with guns and rocket propelled grenades attacked a compound used by the Danish Committee for Aid to Afghan Refugees, or DACAAR, on Monday evening, police said.

Police, aided by villagers, clashed with the attackers in Alishing district for about an hour, leaving three militants wounded, said provincial police chief Abdul Karim. An Afghan driver for the aid group was also wounded in the attack, he said.

Human Rights Watch on Monday accused Taliban militants of committing war crimes by deliberately targeting civilians.

The New York-based rights group said in a new report that nearly 700 Afghan civilians were killed by militants in 2006 -- more than three times the civilian deaths attributed to U.S. and NATO forces, which have been criticized for excessive use of force in civilian areas.

In all, more than 4,000 people died in the Afghan violence last year, according to figures compiled by The Associated Press from Afghan and Western officials. Most were militants killed by U.S.-led coalition and NATO forces,

Unexploded ordinance also remain a danger for Afghans.

On Tuesday, an old artillery shell exploded outside a school compound in the western city of Herat, killing four children and wounding five others, said Noor Khan Nekzad, a spokesman for provincial police chief.

An initial investigation suggested that the blast was accidental and was set off by children playing near the buried device, Nekzad said.

Western Afghanistan saw the last deadly attack on the UN, when militants killed a driver for the UNICEF children's fund in a rocket attack in May 2006.