Several police and prisoners were wounded in the ensuing siege of two prisoners holed up in a workshop inside the sprawling Soviet-era Pul-i-Charki prison compound on the southeast outskirts of Kabul.

"The casualties on our side are five dead, and two police officers are missing. Four militants have been killed and possibly another two are wounded," Lutfullah Mashal, Interior Ministry spokesman, said.

The prisoners killed by guards were Pakistani and Iraqi al-Qaeda members who had been arrested in Kabul by Afghan security forces, Abdul Salam Bakhshi chief of Kabul's Pul-i-Charki prison told Reuters.

The two others, believed to be Pakistanis, were surrounded by police and militia forces armed with machineguns and rocket-propelled grenade launchers, but had managed to keep security forces at bay for more than seven hours.

Two armored vehicles belonging to the German contingent of the Nato-led peacekeeping force stationed in Kabul were standing by outside the walls of the prison, overlooked by four watchtowers on a deserted plain on the outskirts of the capital.

The violence began when one prisoner stabbed and killed a guard, took his gun and opened fire, killing two other guards, Bakhshi said.