Afghan authorities said on Sunday they believe one of the country's police intelligence officers may have been involved in the shooting deaths of two U.S. officers inside the nation's interior ministry a day earlier, prompting NATO to recall all its staff from ministries.

Abdul Saboor, 25, is the main suspect in the killing, which took place at close range well inside the heavily fortified ministry in the center of the capital, Kabul, senior security sources told Reuters on condition of anonymity.

Abdul Saboor is at large right now. He is the main suspect for us, but we cannot draw any conclusions over whether or not he is the killer, one of the sources said, adding that closed-circuit television footage shows that Saboor had access to the command-and-control center where the slain Americans were found.

The killing of the American officers took place as rage gripped the country for a fifth straight day over the burning of the Muslim holy book at a NATO base, despite an apology from U.S. President Barack Obama.

If the shootings are found to be linked to Afghan forces, then new questions will arise about Taliban infiltration into their ranks as well as about their ability to secure Afghanistan once NATO combat forces withdraw in 2014.

The Taliban took responsibility for the American deaths.

Afghan President Hamid Karzai repeated his plea for calm and restraint on Sunday. I hope people will be calm and be assured that we are seriously pursuing this matter, he said of the burning of the Qurans.

Riots across the country killed 29 people and wounded 200 more, Karzai said, including the shooting of two U.S. soldiers by an Afghan army officer who joined the protests earlier in the week.

(Writing by Amie Ferris-Rotman; Editing by Ed Lane)