Afghan security forces battled for five hours against a group of attackers who stormed a government building in the eastern city of Jalalabad after a coordinated assault that killed at least 15 people and wounded 42, local officials said.
Gunmen entered the Finance Directorate in Jalalabad, capital of the Nangarhar province, bordering Pakistan, leading to a three-hour clash, said Attaullah Khogyani, spokesman for the provincial governor.
Fighting between the assailants and Afghan security forces is on-going and one attacker has been killed, he said. "Some of my friends are still stuck there".
Fourty-two people were also wounded. That attack, also claimed by Islamic State, followed much the same pattern as Sunday's incident.
The local officials in eastern Nangarhar province confirm that the coordinated attack on Customs Department in Jalalabad city ended with the elimination of the remaining six militants.
Escalating militant attacks in Afghanistan have left 763 people dead and injured 1,495 others between January and March of this year, according to the quarterly United Nations civilian casualty report released in April.
April saw a series of attacks across the country targeting voter registration centres as Afghanistan gears up for long-delayed legislative elections due in October.
The Taliban recently launched their annual spring offensive, in an apparent rejection of a peace overture by the Afghan government.
Kabul has become one of the deadliest places in the country for civilians as security forces struggle to keep the militants at bay following the withdrawal of North Atlantic Treaty Organisation combat forces at the end of 2014.