DAKAR, Senegal -- Gunfire rang out in the streets of the strategic city of Gao in northern Mali on Sunday, two weeks after French troops appeared to have chased radical Islamists out of the city, which is at the edge of the desert and is the largest population center in the north.
The gun battle between Islamist militants and a force of Malian and French troops, which continued for much of Sunday afternoon, suggested that the quick French campaign against the local Al Qaeda affiliate and its allies was not over, but had entered a new phase of guerrilla warfare.
Sunday's attack by the Islamist fighters was the most serious escalation in the fighting since the French ended over six months of brutal Islamist occupation in Gao at the end of January. That victory came after a quick French bombing campaign and with barely a shot fired.
Continuous bursts of gunfire were heard around the police station, in the city's center and in southern districts as French helicopters hovered overhead. Malian soldiers fought back against Islamists armed with AK-47 rifles as the streets cleared of residents. French troops were also patrolling the city, which has a population of about 86,000, including its surrounding areas.
By late Sunday afternoon, the Islamist fighters had been encircled by French troops, according to a Gao municipal councilor, Abdheramane Oumarou. Later, Mr. Oumarou said that troops had launched a "final assault" on the town's police station, where Islamist fighters had taken refuge, and that it appeared to have been successful.
The Islamists' attack appeared to have begun with an attempted suicide bombing late Saturday night, when a militant on foot blew himself up at a Malian Army checkpoint outside of town, in the second such episode in two days. The bomber's attack, which wounded a Malian soldier, was merely a ruse to allow an Islamist commando unit to enter the city, Mr. Oumarou said.
"The Malian soldiers panicked; that's how the Mujao got into town," Mr. Oumaro said, referring to the Islamist group, the Movement for Oneness and Jihad in West Africa, which is affiliated with Al Qaeda and controlled Gao from May to January. Mr. Oumarou said that the fighters who penetrated Gao were aided by local sympathizers, and that caches of armaments had been discovered by the local authorities.
A Malian Army spokesman said that the bomber was part of a commando team of about 20 Islamist fighters who assaulted a bridge in marshland linking Gao to neighboring villages.
The spokesman, Capt. Daouda Diarra, said the bomber appeared to be of Arab ancestry. He tried to penetrate the army checkpoint, the captain said, setting off his explosives as he did so.
"It's pretty hot in the town right now," said the mayor, Sadou H. Diallo, who was reached by phone on Sunday afternoon. "I can't talk now."
Though the French appeared to be leading the fight on Sunday, primary responsibility for patrols had been handed back to the Malian Army, still shaky after the defeats of last month that led the French to intervene, and which is still plagued by the internecine squabbles that led to a gun battle at a barracks in the capital, Bamako, on Friday.
Embarrassed by the recent events, Mali's interim president, Dioncounda Traoré, apologized to the country's foreign partners in a statement to the state news media. Mali is dependent on large-scale military assistance and other aid from overseas.
The explosion on Saturday night rocked the neighborhood. "We were very scared," said a resident, Halimatou Touré. "There are lots of mujahedeen who come from this area," she said. The bomber's remains were later removed in a wheelbarrow, and French armored vehicles took up positions at the checkpoint.
While Sunday's clashes showed that the northern cities are still vulnerable to attacks from Islamists, the bulk of their force is thought to have taken refuge in the Adrar des Ifoghas, a remote mountain range near Algeria and hundreds of miles to the north of Gao. Troops from France and Chad, supported by French aircraft, are pursuing the Islamists there as well.
Adam Nossiter reported from Dakar, and Peter Tinti from Gao, Mali.
This article originally appeared in The New York Times.