French and Malian troops retook control of Timbuktu, a UNESCO World Heritage site, after Islamist rebel occupiers fled the ancient Sahara trading town and torched several buildings, including a priceless manuscript library.
The US and EU are backing a French-led intervention in Mali aimed at removing the threat of radical Islamist jihadists using the west African state's inhospitable desert north as a springboard for international attacks.
The recovery of Timbuktu followed the swift capture by French and Malian forces at the weekend of Gao.
The major town in the north had also been occupied by the alliance of Islamist militant groups since last year.
The two-week-old mission by France in its former Sahel colony has driven the Islamist rebels northwards out of towns into the desert and mountains.
The operation came after a request from Mali's government but also has wide international support.
Without a shot being fired, 1,000 French soldiers and paratroopers and 200 Malian troops seized Timbuktu airport and surrounded the town on the banks of the Niger River, looking to block the escape of al Qaeda-allied insurgents.
In both Timbuktu and Gao, cheering crowds turned out to welcome the French and Malian troops.
A third town in Mali's vast desert north, Kidal, had remained in Islamist militant hands.
But the secular Malian Tuareg MNLA rebels said they had taken charge in Kidal after Islamist fighters abandoned it.
A Bamako-based diplomat confirmed the MNLA takeover of Kidal, saying the Tuaregs were likely to try to press long-standing demands for autonomy for their northern region.
A French military spokesman said the assault forces at Timbuktu were being careful to avoid combat inside the city so as not to damage cultural treasures and mosques and religious shrines in what is considered a seat of Islamic learning.
But Timbuktu Mayor Ousmane Halle reported that departing Islamist gunmen had set ablaze a South African-funded library in the city containing thousands of invaluable manuscripts.
"The rebels set fire to the newly-constructed Ahmed Baba Institute built by the South Africans ... This happened four days ago," Mr Ousmane told Reuters by telephone from Bamako.
He said he had received the information from his chief of communications who had travelled south from the city a day ago.
Mr Ousmane was not able to immediately say how much the concrete building had been damaged. He added the rebels also set fire to his office and the home of a member of parliament.
UNESCO spokesman Roni Amelan said the Paris-based UN cultural agency was "horrified" by the news of the fire, but was awaiting a full assessment of the damage.
Marie Rodet, an African history lecturer at Britain's School of Oriental and African Studies, said Timbuktu held one of the greatest libraries of Islamic manuscripts in the world.
"It's pure retaliation. They (the Islamist militant rebels) knew they were losing the battle and they hit where it really hurts," Ms Rodet told Reuters.
"These people are not interested in any intellectual debate. They are anti-intellectual."
The Ahmed Baba Institute, one of several libraries and collections in Timbuktu containing fragile documents dating back to the 13th century, is named after a Timbuktu-born contemporary of William Shakespeare and houses more than 20,000 scholarly manuscripts.
Some were stored in underground vaults.
The French and Malians have encountered no resistance so far at Timbuktu, but they face a tough job of searching the labyrinth of ancient mosques and monuments, and mud-brick homes between alleys to flush out any hiding Islamist fighters.