KANDAHAR, Afghanistan — About 870 prisoners escaped during a Taliban bomb and rocket attack on the main prison in southern Afghanistan that knocked down the front gate and demolished a prison floor, Afghan officials said today.

The police chief of Kandahar province, Sayed Agha Saqib, said 390 Taliban prisoners were among those who fled the prison during the attack late Friday.

NATO's International Security Assistance Force put the number of escapees slightly higher, at around 1,100, according to spokesman Brig. Gen. Carlos Branco. He conceded that the assault was a success.

"We admit it," Branco said. "Their guys did the job properly in that sense, but it does not have a strategic impact. We should not draw any conclusion about the deterioration of the military operations in the area. We should not draw any conclusion about the strength of the Taliban."

The complex attack included a truck bombing at the main gate, a suicide bomber who struck a back wall and rockets fired from inside the prison courtyard, setting off a series of explosions that rattled Kandahar, the country's second biggest city.

The rockets demolished an upper prison floor, said Mohammad Qasim Hashimzai, a deputy minister at the Justice Ministry. Nine police were killed in the attack, said Interior Ministry spokesman Zemeri Bashary.

There were no indications that the militants received help from the inside, but as a precaution the prison's chief official, Abdul Qabir, was placed under investigation for possible involvement, Hashimzai said.

NATO was providing intelligence, surveillance and reconnaissance assets to help track fleeing militants, Branco said.