Afghan forces are fighting to regain control of the city of Kunduz after it became the first provincial city to be seized by the Taliban since the 2001 US-led invasion.
US military planes have also hit Taliban positions on the outskirts of the city.
The sudden fall of Kunduz on Monday was a major setback for the government of President Ashraf Ghani and raised questions over the ability of Afghan forces to tackle the Islamist insurgency alone.
President Ghani said today that government reinforcements had reached Kunduz and an army battalion was on its way to help troops regain the city.
He said the security forces had been hampered by Taliban fighters using civilians as human shields.
Earlier, the government said its forces had regained the city prison and the provincial police headquarters.
More than 100 Taliban fighters were among the 600 prisoners who escaped during the jail attack, security chief Rahmatullah Nabil said.
It is not known how many people have been killed in the fighting, but the president said “the enemy is suffering heavy casualties from air strikes”.
Afghan Defence Minister Mohammad Masoom Stanekzai said 17 members of the security forces had been killed and 18 wounded in the last 24 hours across the country.
Taliban spokesman Zabihullah Mujahid said three militants had died and 11 were wounded, while at least 18 Afghan police had been killed.