Northern Alliance says the mutiny will not last long
A BBC correspondent at the scene says fewer than 10 of the hundreds of Taleban originally taken prisoner may still be alive, on the third day of the revolt.
US warplanes launched up to 30 air strikes overnight against the fighters, who were originally detained following their surrender in Kunduz over the weekend.
Northern Alliance fighters have been seen scrambling up the ramparts of the fort in the past few hours.
Several vans carrying British and American special forces have arrived to co-ordinate the onslaught.
At one point on Monday, an American bomb went astray, killing six Northern Alliance fighters and seriously injuring five US soldiers.
The hurt men were among a number of American special forces inside the fort who are helping to co-ordinate the response of the Northern Alliance.
The alliance had detained about 500 non-Afghan Taleban prisoners in the Qala-e-Jhangi fortress.
The revolt began on Sunday when the prisoners killed some of their guards with guns they had reportedly smuggled into the fort, and seized more weapons.
Some reports say they then attempted a mass breakout.
The International Committee for the Red Cross has been trying to visit the fort to assess the situation.
US casualties
Several hundred Northern Alliance fighters and Taleban prisoners have been killed. US Defence Secretary Donald Rumsfeld said some Taleban had managed to escape.
Alliance soldiers emerging from the fort have been describing a bloodbath.
The injured US soldiers have been evacuated to Uzbekistan, said General Richard Myers, chairman of the US Joint Chiefs of Staff, in Washington.
One CIA operative is reported to have died.
A journalist who was near Mazar-e-Sharif during the initial stages of the revolt said American and British special forces went into the fort because they thought an American soldier there had been killed, and another had run out of ammunition.
Denial of opportunism
Abdul Wahid, a Northern Alliance spokesman, denied his group was using the uprising as an opportunity to get rid of unwanted prisoners, and stressed the alliance was aware of its international obligations.
The prisoners are mainly Arabs, Chechens and Pakistanis linked to Osama Bin Laden's al-Qaeda network.
Foreign fighters, who are locally regarded as destabilising elements in the country, have often been beaten or killed when territory has fallen to the Northern Alliance in the course of the current conflict.
Alliance commanders said the remaining prisoners, trapped in a tower, were running out of ammunition and would not last long.