KABUL, Afghanistan -- A suicide bomber blew himself up in eastern Afghanistan on Saturday as mostly Taliban fighters gathered to celebrate a three-day cease-fire marking the Islamic holiday of Eid al-Fitr. The bombing killed at least 25 people, according to local officials.

Attaullah Khogyani, spokesman for the governor of Nangarhar province, where the attack occurred, said 45 people were also wounded in the suicide attack, which was claimed by the Islamic State of Iraq and Syria (ISIS) branch in Afghanistan.

Nangarhar provincial Police Chief Ghulam Sanayee Stanikzai said most of the dead and wounded were believed to be members of the Taliban.

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The Reuters news agency said ISIS had claimed responsibility for the attack in a statement posted on Amaq, the terror group's multimedia mouthpiece. ISIS fighters have clashed with the Taliban, which has rejected the former group's demands for an Islamic "caliphate," ruled under a harsh interpretation of shariah law, to be established in Afghanistan .

The devastating explosion came as previously unthinkable scenes of unarmed Taliban fighters celebrating Eid, often alongside Afghan security forces, played out in cities throughout the war-shattered country on Friday and then again on Saturday.

Within hours of the explosion on Saturday, President Ashraf Ghani announced he would extend a nine-day cease-fire that had been set to expire on Sunday and which he had unilaterally announced last week. The cease-fire was to end at the conclusion of the Eid holiday, which follows the month-long fasting month of Ramadan.

Ghani offered no details of the extension, including how long it would be in effect. The Taliban's leader, Haibatullah Akhunzada, on Monday separately announced a three-day truce to mark the Eid holiday. The Taliban cease-fire took effect at midnight on Thursday.

Ghani, in his statement announcing the extension, called on the Taliban to reply in kind. He also said that a cease-fire could be accompanied with visits to their prisoners and treatment for their fighters at hospitals in Afghanistan. Ghani also repeated his promise that everything could be on the negotiation table, including the presence of foreign forces.

Earlier this week Taliban leader Akhundzada said he wanted direct talks with the United States before engaging in negotiations with the Afghan government. There was no immediate Taliban reply to Ghani's latest offer of an extension.

Meanwhile Atta-ul-Rahman Salim, deputy head of Afghanistan's High Peace Council, said Taliban fighters from across the country were entering into government-controlled areas to visit their families "and they were being welcomed by government security forces."

In eastern Logar province, dozens of Taliban on motorcycles roared through the provincial capital of Pul-e-Alam, some of the vehicles festooned with the Afghan flag. Provincial police spokesman Shahpur Ahmadzai told The Associated Press that the Taliban were unarmed and no one was allowed into the city with weapons.

Abdullah Faizani, a Taliban fighter from Logar's Baraki district, said it had been seven years since he has been to the provincial capital.

Although he wanted an extended cease-fire, he said he would not lay down his weapons permanently until "all the foreign troops leave Afghanistan."

In northern Kunduz province, Doctor Abdul Majhid said nearly 2,000 Taliban were seen celebrating in the city, many of them with family and friends but also several were seen celebrating with Afghan Security Forces.

"We are feeling that these days are golden days for us, it is so peaceful," said Majid.

In southern Kandahar, Haji Gulalai said he welcomed the cease-fire.

"I'm so happy for the cease fire in Afghanistan, and I am hoping peace forever."

In Afghanistan's northern Baghlan province, Asadullah Shabaz, head of the provincial council, said unarmed Taliban joined in prayers at a local mosque.

"We are all just so tired of war," he said.