WASHINGTON (REUTERS) - The US military confirmed on Friday that a British hacker who was one of the Islamic State in Iraq and Syria (ISIS) movement's top computer experts and who was active in encouraging people abroad to carry out "lone wolf" attacks has been killed in Syria by a US air strike.

Junaid Hussain of Birmingham, England, was killed on Aug 24 by a US military air strike on the Islamic State stronghold of Raqqah, Syria, Air Force Colonel Pat Ryder, a spokesman for US Central Command, told reporters.

Hussain had been involved in "actively recruiting ISIL sympathisers in the west to carry out 'lone wolf' style attacks," Ryder said, using another acronym for the militant group that has seized large parts of Syria and Iraq.

"We have taken a significant threat off the battlefield and have made it very clear that in terms of ISIL leadership, we are going to target them where we can," Ryder said.

Hussain was responsible for releasing personal information of around 1,300 US military and government employees in recent weeks, and "sought to encourage" attacks against them, US officials said.

One official said Hussain had also been linked to the release of the names, addresses and photos of 100 US service members on an ISIL website in March.

It was the second killing of a senior Islamic State figure by US forces in the last 10 days.

Islamic State's second-in-command was killed in a US air strike near Mosul, Iraq, on Aug 18.

The strike that killed Hussain was among the first directed specifically at an individual involved mainly in Islamic State's extensive cyber and social media campaigns.

US and European officials stressed that Hussain had also played a larger operational role within ISIL, helping target attacks, recruiting and logistics.

"This individual was very dangerous. He had significant technical skills, and he had expressed a strong desire to kill Americans, and recruit others to kill Americans," Ryder said.

US officials said Islamic State's efforts at hacking into computer systems have largely been quite primitive.

But the group's use of social media and the Internet to promote its cause and recruit and inspire foreign fighters to join ISIS in Syria or carry out attacks in their own countries has been effective.

Hussain left Britain to join the Islamic State some time in the last two years. He was jailed by British authorities in 2012 for hacking former British Prime Minister Tony Blair's address book from an account maintained by a Blair adviser.