Afghan security forces inspect the site of attack on British charity Save the Children office.— AFP
Mohammad Amin, who was inside the compound when the attackers launched the raid at 9:10am (0440 GMT), told AFP from his hospital bed that he heard “a big blast”.
“We ran for cover and I saw a gunman hitting the main gate with an RPG (rocket-propelled grenade) to enter the compound. I jumped out of the window,” Amin said.
Afghan TV news channels showed a thick plume of black smoke rising above the compound and what appeared to be at least one vehicle on fire outside the office.
IS has intensified attacks in cities in recent months, targeting mosques and Afghan security forces as it expands beyond its stronghold in the east.
Militant groups rarely claim responsibility for attacks on aid workers.
Charities targeted
Wednesday's assault comes days after Taliban gunmen stormed a luxury hotel in the Afghan capital and killed at least 22 people, mostly foreigners.
Insurgents armed with Kalashnikovs and suicide vests attacked the landmark Intercontinental Hotel, going from room to room searching for foreigners during the more than 12-hour ordeal.
“Attacks directed at civilians or aid organisations are clear violations of international humanitarian law and may amount to war crimes,” the UN's mission in Afghanistan tweeted earlier.
The assault on Save the Children, which has operated in Afghanistan since 1976, is the latest violence to hit a foreign aid group in the country.
Afghanistan recorded the second highest number of attacks against aid workers worldwide in 2016, according to UK-based research group Humanitarian Outcomes. Only South Sudan was more dangerous.
The International Committee of the Red Cross announced in October it would “drastically” reduce its presence in Afghanistan after seven employees were killed in attacks last year.
Nangarhar, a restive province bordering Pakistan, is a stronghold for IS and also has a significant Taliban presence.
US and Afghan forces have been carrying out ground and air operations against IS fighters in the province. While Afghan security forces are conducting most of the fighting against IS and Taliban militants, US troops operate alongside them in a training capacity and are frequently on the front lines.
The last major attack in Jalalabad was on December 31 when an explosion at a funeral killed 18 mourners and wounded 13. There was no claim of responsibility.