KABUL: A roadside bomb tore through a minibus carrying people to a wedding celebration in northern Afghanistan on Friday, killing at least 19 people and wounding 16, authorities said.    

The blast underscored the heavy toll the war has taken on civilians who are frequently caught up in the fighting between insurgents and Afghan and foreign security forces.

The bus was taking guests to a wedding celebration in the Dawlat Abad district of the northern Balkh province, about 450 kilometers (270 miles) northwest of the capital, Kabul, police spokesman Shir Jan Durani said.

District police commander Bismullah Muslimyar gave the death toll and said six children and seven women were among those killed in the 6 a.m. blast.

He said a police patrol had passed through the area during the night.

Muslimyar said the wedding had occurred Thursday, and the party was heading to the groom's home to congratulate the newlyweds according to tradition.    Afghan President Hamid Karzai strongly condemned the attack.

''Planting a mine on a road used by civilians and the killing of innocent people represents hostility toward humanity,'' he said in a statement.

Earlier this month, the UN Security Council expressed serious concern at the high number of civilian casualties in the war, especially among women and children.

The Taliban and other militants are responsible for the overwhelming majority of civilian deaths in the country. About 77 per cent of the deaths between January and June can be attributed to insurgents, a UN report said.

Insurgent-placed homemade bombs continue to be the deadliest weapon for civilians, accounting for 29 per cent of all such deaths in the period, it said.

Meanwhile, Nato's visiting top official urged the Afghan government to ensure that the next presidential elections in 2014 are free and fair. Karzai will not be able to run after having served the maximum two terms in office.

''It's essential for the trust between the Afghan people and government that these elections take place in a free, transparent and inclusive manner,'' Secretary-General Anders Fogh Rasmussen said in the northern city of Mazar-i-Sharif where he and envoys from Nato's governing body were concluding a two-day visit to Afghanistan.

There is mounting uncertainty about the upcoming transfer of power, which will come as Nato's troops prepare to end their combat role at the end of 2014.

Many Afghans already view their government as weak and corrupt and there are fears that the upcoming elections will not be fair.

Many foreign observers said the presidential ballot in 2009 was characterized by massive fraud.    Separately, six football fans died and 36 were injured Friday when their bus collided with a fuel tanker on a narrow road about 400 kilometers (240 miles) northwest of the capital, provincial governor Mohammad Aleem Saaie said.

The fans were traveling to Kabul for the final round of the country's football championships.