There was no immediate claim of responsibility for the suicide attack in Jalalabad city, outside the office of the Nangarhar provincial governor.
Najibullah Kamawal, director of the health department in the eastern Nangarhar province, said another 65 people were wounded in Saturday's attack.
No surprisesThe first formal nationwide ceasefire since the 2001 United States invasion had been widely welcomed across the country as Afghans - Taliban, security forces and civilians - celebrated Eid, the holiday that caps the fasting month of Ramadan.
Dozens of unarmed Taliban militants had earlier entered the Afghan capital and other cities to celebrate Eid and the end of Ramadan.
Some have criticized his move, which allowed the Taliban to flow into cities across the country, though the militants said they would withdraw by sunset on Sunday.
"They are unarmed, as they handed over their weapons at the entrances", Kabul police spokesperson Hashmat Stanekzai told Reuters.
The Taliban have steadily expanded their presence in recent years, seizing a number of districts across the country and carrying out near-daily attacks on Afghan security forces.
Taliban fighters and security forces embraced and took selfies with each other over the first two days of the Eid holiday.
The Afghan Taliban had announced that its three-day ceasefire will indeed end at midnight local time Sunday, dispelling reports that it might be extended.
Ghani´s extension of the government´s eight-day ceasefire, which had been due to expire Tuesday night, drew immediate worldwide support and calls for the Taliban to follow suit.
Stephen Hawking's voice will be beamed into space toward 'nearest black hole'
Kip Thorne, a Nobel prize-winning American physicist, paid tribute to "by far the most stubborn friend I ever had". A memorial stone will lie above inscribed, "Here lies what was mortal of Stephen Hawking 1942 - 2018".
European Union's High Representative/Vice-President Federica Mogherini also said in a statement that the "historic ceasefire between the Afghan government and the Taliban during Eid al-Fitr has given the Afghan people a much-needed respite from 17 years of conflict". They have also demanded the withdrawal of all foreign forces.
The Taliban leader in Afghanistan, Mullah Hebatullah Akhundzada, said in an Eid address that his group wanted to see the USA military and other foreign forces leave Afghanistan. They said foreign forces were exempted from their promise not to attack.
That came after Ghani announced that police and troops would cease operations against the Taliban for eight days, starting last Tuesday - though he warned that operations against other militants, including Daesh, would continue.
The Taliban are fighting USA -led North Atlantic Treaty Organisation forces, combined under the Resolute Support mission, and the US -backed government to restore Shariah, or Islamic law, after their ouster by US -led forces in 2001. Most of the dead and wounded were believed to be Taliban, he said. Rampant corruption in the Afghan government and a long tug-of-war within the US-brokered national unity government has had a negative impact on the government's efforts to eradicate terrorism.
Many people across the country have urged the government and the Taliban to extend their ceasefires, which follow months of deteriorating security, especially in the capital Kabul.
U.S. Secretary of State Mike Pompeo, echoing Ghani's announcement on Saturday, said peace talks would have to include a discussion on the role of "international actors and forces".
The United States wants Pakistan, which it accuses of harbouring Afghan Taliban commanders, to exert more influence on the group to bring it to the negotiating table.
"We have held the ceasefire well so far".
The only time direct talks between the Afghan government and the Taliban have been held, in 2015, they broke down nearly immediately.