A local district chief and dozens of his relatives were at the ceremony in the Dur Baba district of Nangarhar province.

"My brother saw the bomber and grabbed him just as he pushed the button, killing him and many others," Gul told Reuters from a hospital bed in Jalalabad, Nangarhar's capital.

Khan Mohammad, also in hospital in Jalalabad after being wounded in the attack, said: "I was at the graveyard just putting the dead body inside the tomb when I heard a loud explosion. Many people were screaming and crying for help."

The provincial governor's spokesman, Ahmadzia Abdulzai, said the attack was aimed at Gul and his supporters because they had recently opposed insurgents in the area. The funeral was for one of Gul's relatives.

"We have at least 25 innocent people martyred and around 65 others wounded," Abdulzai said. NATO also put the death toll at 25, but said more than 50 were people wounded.

The Interior Ministry blamed Taliban insurgents for the bombing.

President Hamid Karzai condemned the attack and offered his condolences to the victims' families, he said in a statement.

Despite the presence of hundreds of thousands of Afghan and foreign troops fighting the Taliban-led insurgency, violence is at its worst since the were toppled by Afghan and US forces in late 2001, five years after they took power.

Tuesday's attack was carried out days after 15 young men and two young women were beheaded in the southern Helmand province, punishment meted out by Taliban fighters for a mixed-sex party with music and dancing.

On Saturday, a twin suicide bomb attack targeting a NATO base in the eastern province of Wardak killed 12 people, eight civilians and four policemen.

Suicide attacks and roadside bombs are the biggest killers of Afghan civilians as well as Afghan and foreign soldiers.