A Taliban source has confirmed that opposition forces have entered Mazar-e-Sharif.
The advance represents a major victory in the US-led campaign.
Earlier, Rashid Dostum, the Uzbek warlord who controlled Mazar-e-Sharif until the Taliban captured the city three years ago, said the alliance overran the city in a half hour.
"Right now it is calm," he said in the strategically vital city.
Opposition spokesman Ashraf Nadeem said in a telephone interview that the Taliban appeared to have abandoned the city. He said opposition forces had broken through Taliban defences at the Pul-e-Imam Bukhri bridge on the southern edge of the city, overran the airport and entered the city.
‘‘We are moving through one neighbourhood at a time,’’ he said.
He said he was speaking by satellite telephone from a hill overlooking Mazar-e-Sharif. Dostum claimed northern alliance forces killed 500 Taliban fighters and took hundreds of others prisoner during the past four days of fighting.
Dostum claimed the alliance suffered 28 killed and more than 30 wounded.
There was no way to confirm the casualty claims, which both sides have exaggerated in the conflict.
Taliban troops appeared to be retreating east toward Samangan province, Dostum said.
Re-taking Mazar-e-Sharif from the Taliban would open up vital supply lines to the opposition alliance from Uzbekistan and Tajikistan. The population of the city - which is located at a strategic crossroads in the north - is largely made up of ethnic Uzbeks and Tajiks, the same minorities as many in the opposition coalition.
Ghulam Reza Zada, a spokesman for the Shiite Muslim faction involved in the opposition advance, also said opposition forces were entering the city but did not know whether all Taliban fighters had withdrawn.