The killing of an American who directed al Qaeda's media campaign from his Pakistani hideout is likely to be a big blow for the militants, especially as they wage a propaganda war with Islamic State.

American al Qaeda member Adam Gadahn, who faced treason charges in the United States, was killed early this year in a strike on an al Qaeda camp in Pakistan, near the Afghan border, U.S. officials said on Thursday.

"He was highly important. He was the man on their media front line," said Ahmed Rashid, a Pakistani author and expert on the Taliban and A- Qaeda.

"Given the success of ISIS in media and social media, he would have been much needed, especially in communicating with English-speaking audiences and on web sites and so on," he said, referring to Islamic State.

Gadahn, for whom the United States had offered a reward of $1 million, was believed to be in his late 30s. Born in Oregon, he grew up in California, converted to Islam at 17 and became a spokesman and translator for Al-Qaeda.

When the United States accused him of treason in 2006, he became the first person to face such charges since the World War Two era, according to the U.S. Justice Department.

Gadahn has been involved with Al-Qaeda's as-Sahab media wing and had appeared in its videos wearing robes and a turban and warning the United States it would face attacks if it did not heed Al-Qaeda demands.

"He was the main man in charge of the Al-Qaeda narrative, so his death will have an impact on the propaganda machine," said Amir Rana, author of a book on militant groups in Pakistan.