Militants stormed the offices of Save the Children in eastern Afghanistan on Wednesday, killing four people and triggering a shootout with police that lasted almost 10 hours, provincial officials and the organization said.
The terrorist group ISIS claimed responsibility for the attack in Jalalabad, the capital of Nangarhar province. Among the four killed were two staffers of the NGO, a security guard who also worked for Save the Children and an Afghan army soldier.
The assault started with a suicide bomber who detonated his explosives' vest at the provincial offices of Save the Children, said Attahullah Khogyani, spokesman for the provincial governor.
Security forces killed four other attackers, he said, adding that at least 26 people, including three members of the Afghan security forces, were wounded.
After eight hours the fighting subsided and Khogyani said he initially thought it was over but then the shooting picked up again.
Two hours later, it was finally over, he said.
Carolyn Miles, president of Save the Children, expressed "profound sadness" at the killing of the NGO's three employees in Jalalabad. She said four wounded staffers were receiving medical treatment.
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"We are shocked and appalled at the violence, carried out against our staff in Afghanistan who are dedicated humanitarians, committed to improving the lives and wellbeing of millions of children across the country," Miles said.
Miles added that the organization had been working in Afghanistan since 1976, "providing life-saving health, education, nutrition and child protection programs that have helped millions of children." Save the Children also said it had temporarily suspended its work across Afghanistan.
In a statement on its Aamaq media arm, the 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.
Khogyani said the security forces had managed to rescue 46 people, mostly employees of the Save the Children, as the attack unfolded.
U.S. State Department spokeswoman Heather Nauert denounced the assault, calling it "heartbreaking" and offered "deepest condolences to the victims and families."
U.N. Secretary-General Antonio Guterres was "appalled and deeply saddened" by the attack on the Save the Children office, U.N. spokesman Stephane Dujarric said.
"Humanitarian organizations provide life-saving assistance to the most vulnerable men, women and children in Afghanistan," Dujarric told reporters at U.N. headquarters in New York. "Aid workers, and their premises and assets, should never be a target."
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."
"Increased violence has made operating in Afghanistan difficult for many organizations," she said.
Amnesty International's chief for South Asia, Biraj Patnaik, expressed solidarity with Save the Children.
"Bombing and shooting people who are working for no other reason than to help improve the lives of young Afghans is a cowardly and despicable act," Patnaik said.
The attack followed 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.
Eleven of the 14 foreigners had been previously identified as working for the private Afghan airline KamAir. During a ceremony at Kabul's airport on Wednesday, the bodies of seven Ukrainian citizens were handed over to officials for transfer to Ukraine.
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.
Associated Press writer Amir Shah in Kabul, Afghanistan, contributed to this report.