A suicide bomber blew himself up in a crowd of Afghan Taliban, security forces, and civilians celebrating an unprecedented ceasefire in the war-torn country on Saturday, killing at least 20 people, officials said.

The attack came as President Ashraf Ghani announced an extension of the government's week-long ceasefire with the militant group after both sides agreed to halt hostilities for Eid.

There was no immediate claim of responsibility for the blast that also wounded at least 16 others marking the suspension of fighting in Rodat district of Nangarhar province, but an Afghan security source told AFP that the Islamic State group was to blame.

"A suicide bomber detonated among people, security forces and Taliban who were celebrating the ceasefire," provincial governor spokesman Attaullah Khogyani told AFP.

He said at least 20 people had been killed and 16 others wounded. Provincial health director Najibullah Kamawal confirmed the death toll but said 25 wounded had been taken to hospital.

Ghani made his announcement in a rare televised address to the nation, in which he also asked the Taliban to extend their three-day ceasefire which is due to end Sunday.

"I order the security forces to remain on their defensive positions," Ghani said, adding details of the extension would be released later.

The government's ceasefire, which was due to end Tuesday, did not include IS.

On the first two days of Eid, Taliban fighters, Afghan security forces and civilians hugged and took selfies with each other across the country, in an outpouring of emotion over the ceasefire.

'Tired of war' 

In the contested district of Bati Kot in Nangarhar, Taliban fighters carrying assault weapons and rocket-propelled grenade launchers travelled by car and motorbike, waving Afghan and Taliban flags.

Afghan forces manning checkpoints offered Eid greetings to the fighters, embracing and posing for photos with the same people they are usually trying to kill -- a scene that would have been unthinkable only a few days ago.

The unusual bonhomie between the two sides came as Ghani confirmed that Pakistani Taliban chief Maulana Fazlullah had been killed in a US drone strike.

US forces targeted Fazlullah in a counterterrorism strike on Thursday in eastern Kunar province, close to the border between Afghanistan and Pakistan, US officials said, without confirming his death.

Ghani said Pakistani leaders had assured him the strike was a "great step toward building trust between the two nations," while urging them to "bring (the) Afghan Taliban residing in Pakistan to the negotiation table."

On Tuesday, Army Chief of Pakistan General Qamar Javed Bajwa visited Kabul where he met with Ghani.