"Attackers entered the compound and the fight is going on".
"An explosion rocked the area and right after that children and people started running away", Ghulam Nabi, who was nearby when the bomb exploded, said.
Press Secretary of the Governor of Nangarhar province said the attack happened around 09:10 local time on Wednesday when a suicide bomber blew up a auto at the entrance to the office of the organization.
The officials are saying that the attack was carried out by a group of five insurgents with one of them initially detonating a vehicle packed with the explosives near the NGO office.
During the attack inside the building was more than fifty employees.
Friendly fire kills 11 in Iraq air strike
Two senior Iraqi Army officers said the USA forces had thought the victims were militants, the Associated Press reported. Last month Iraq declared victory over the extremists but continues to fight IS insurgent groups across the country.
"All other staff have been safely rescued from the office", Save the Children president and CEO Carolyn Miles said.
"Our primary concern remains to secure the safety of all of our staff", a group representative said in an emailed statement.
Save the Children has been working in Afghanistan since 1976 providing life-saving health, education, nutrition and child protection programs that have helped millions of children. While no group has claimed responsibility for the attack.
The attack comes just three days after the Taliban gunmen raided a luxury hotel in Kabul, killing at least 22 people, mostly foreigners. An attack in December on a cultural center killed at least 41 people.
And in Jalalabad last month, a motorcycle-riding suicide bomber struck outside a soccer stadium in the city, killing at least six people and wounding 13.
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