Afghanistan's security service is denying claims that the suicide bomber who killed two American troops and four Afghans in a weekend attack was a member of the country's intelligence agency, The Associated Press reports.

The service's spokesman, Shafiqullah Tahiri, said Tuesday, Oct 16, the attacker wore an Afghan uniform to gain access to the intelligence headquarters in Kandahar's Maruf district.

Tahiri says the attacker blew himself up as a group of NATO troops and Afghans were arriving to deliver new office furniture to the facility on Saturday.

NATO and Afghan officials had said the bomber was a member of Afghanistan's National Directorate of Security.

The growing number of insider attacks has raised doubts whether Afghan forces will be able to effectively control security after foreign troops depart in 2014.