France bombed Islamist targets in northern Mali on Monday following a string of guerrilla attacks by the extremists a month after Paris launched an offensive to drive them from its former colony.

In a pre-dawn attack, witnesses said a French army helicopter destroyed a central police station in the northern city of Gao from where rebels from the Movement for Oneness and Jihad in West Africa (MUJAO) had opened fire from the station on Malian troops Sunday, sparking an hours-long street battle.

An AFP reporter at the scene said the building was destroyed and body parts were lying in the debris.

One witness said an Islamist fighter inside the building had blown himself up.

Along with back-to-back suicide bombings Friday and Saturday, also claimed by MUJAO, the latest fighting underlined the threat of a deepening insurgency one month after France began its offensive.

France launched its operation on January 11, responding to a cry for help from Mali's interim government by sending in fighter jets, attack helicopters and ground troops to battle Al-Qaeda-linked Islamist groups that had seized control of the north for 10 months and were advancing into southern territory.

The intervention racked up a string of early successes as French-led forces drove the extremists from Gao, Timbuktu and the rest of the towns under their control.

But deadly landmine explosions and the suicide attacks and fighting in Gao show the deep security problems still facing Mali -- and by extension France, which is eager to wind down the operation and hand over to a United Nations peacekeeping mission.

Paris announced last week it would begin bringing its troops home in March, though President Francois Hollande -- who received a hero's welcome when he visited Mali at the beginning of the month -- has promised to stay as long as necessary.

European Union international development and aid ministers are due to meet in the Irish capital Dublin on Monday, with help for Mali high on the agenda.

Sunday's attack was the first large-scale urban guerrilla assault on territory reclaimed by French-led forces.

It started early in the afternoon when Malian soldiers clashed with Islamists in the city centre, near the governor's offices and the police station, which the rebels had used as the headquarters of their "Islamic police" until French-led forces recaptured Gao on January 26.

A witness said the gunmen had hidden in the empty police station then attacked Malian soldiers when they arrived, as snipers hidden in surrounding buildings opened fire.

He said that after a fierce gunbattle, French troops had intervened.

Residents ran for cover as Kalashnikov bullets and 14.5-millimetre rounds pierced the air.

Rocket-propelled grenade explosions and fire from heavy machine guns and light weapons resounded late into the afternoon before dying down in the evening, when a power cut plunged the city into darkness.

It was not immediately possible to establish a death toll. A Malian army officer said "many" Islamists had been killed.

One security source said several dozen insurgents had been involved in the attack.

Claiming the attack, MUJAO's spokesman Abou Walid Sahraoui said: "The combat will continue until victory, thanks to God's protection.

"The mujahedeen are in the city of Gao and will remain there."

Mali imploded after a March 22 coup by soldiers who blamed the government for the army's humiliation at the hands of north African Tuareg fighters, who have long complained of being marginalised by Bamako.

With the capital in disarray, Al-Qaeda-linked fighters hijacked the Tuareg rebellion and took control of the north, imposing a strict vision of Islamic law and punishing offenders with public whippings, amputations and executions.