The raid followed a string of assassinations in the once peaceful north of the country, and came one day after the beginning of the Muslim fasting month of Ramadan.

One attacker detonated a car bomb at the gates of the guesthouse. The other two stormed the building where they fought Afghan forces for a couple of hours before detonating their explosives, said Kunduz police detective Abdul Rahman.

Ten people, including civilians and a police officer, were wounded in the early morning attack, said Rahman. It was not immediately clear if any foreigners were among the wounded.

Rahman said the slain Afghan security guards were employed by German development agency GTZ.

The Taliban claimed responsibility for the attack, said spokesman Zabihullah Mujahid.

Violence has intensified in the north of the country in the past year as insurgents seek to demonstrate their reach beyond their traditional southern heartland around Kandahar city.