Two security guards and a civilian were killed when ISIS militants stormed the offices of Save the Children in eastern Afghanistan on Wednesday, triggering a shootout with police that was still underway more than eight hours later.

The Islamic State group claimed responsibility for the attack that began when a suicide car bomb detonated outside the office in Jalalabad around 9:00 a.m. local time.

A group of gunmen stormed the compound of the non-government organization where Afghan Special Forces engaged them in a shootout.

“An explosion rocked the area and right after that children and people started running away,” said Ghulam Nabi, who was nearby when the bomb exploded, told Reuters. “I saw a vehicle catch fire and then a gunfight started.”

Government spokesman Attaullah Khogyani said police killed two of the attackers, and that at least 26 people, including six police officers, were wounded.

After eight hours the fighting subsided and Khogyani said he initially thought it was over but then the shooting picked up again. Save the Children confirmed the attack was still ongoing.

"Our primary concern is to secure the safety of all of our staff," it said, adding that it had temporarily suspended its work across Afghanistan.

In a statement on its Aamaq media arm, ISIS said one of its suicide bombers with an explosive-laden vehicle and a subsequent raid targeted “British and Swedish foundations and Afghan government institutes.”

Both the Taliban and ISIS are active in eastern Nangarhar province. Earlier on Wednesday, a Taliban spokesman said the group was not involved in the attack.

Zabihullah Zemarai, a member of the provincial council in Nangarhar, said police forces managed to rescue more than 40 people, mostly employees of the Save the Children group as the attack unfolded.

Monica Zanarelli, the International Committee of the Red Cross' head of delegation in Afghanistan, said that an attack against an organization that helps children is "outrageous."

"Civilians and aid workers must not be targeted," she said in a statement. "Increased violence has made operating in Afghanistan difficult for many organizations."

The attack follows a deadly weekend siege of the Intercontinental Hotel in the capital Kabul in which 22 people were killed, including 14 foreigners. Multiple U.S. citizens were killed and injured in the Taliban's 13-hour siege of the hotel, the State Department said Tuesday. No exact figures were immediately available for either the U.S. fatalities or injuries.

Mirwais Samadi, head of the consulate department at Afghanistan's Foreign Ministry, said the Kabul attack was launched by "terrorists" and their supporters.

"Some of our countrymen were martyred and some foreign nationals also were killed," he said. "We express our condolences and thoughts to the victims and families."

In eastern Ghazni province, meanwhile, four Afghan policemen were killed after their checkpoint came under attack by insurgents, said Arif Noori, spokesman for the provincial governor.

Six insurgents were killed and three were wounded in the battle, which took place early on Wednesday morning in Dayak district, said Noori.

Fox News' Benjamin Brown and The Associated Press contributed to this report.