* Repeated gunfire heard in the recently recaptured town
* Islamist rebels have infiltrated Gao, Malian officer says
* Suicide attack targeted same Gao checkpoint hit on Friday
* As French hunt in mountains, fears of guerrilla war emerge (Updates with gunbattles in Gao, quote)
By David Lewis
GAO, Mali, Feb 10 (Reuters) - Malian government troops fought gunbattles with Islamist insurgents in the streets of the northern town of Gao on Sunday, highlighting fragile security in zones recently recaptured by a French-led military offensive.
Gunfire resounded through the sandy streets and mud-coloured houses of the ancient town on the Niger River, just hours after French and Malian forces reinforced a checkpoint that was attacked for the second time in two days by a suicide bomber.
"Islamists who have infiltrated the town are trying to attack our positions. But we're fighting back," a Malian army officer told Reuters by phone. Residents and a Reuters reporter in Gao said they heard bursts of gunfire and detonations.
A Reuters TV cameraman saw a figure clad in black robes and a black turban carrying a bag and running to avoid heavy gunfire from the soldiers. One Malian soldier said some of the rebel infiltrators were on motorbikes.
A fast-moving French military intervention launched last month in its former Sahel colony has driven al Qaeda-allied fighters from Mali's main northern towns, such as Gao and Timbuktu, into the northeast Adrar des Ifoghas mountains.
But with Mali's weak army unable to secure recaptured zones, and the deployment of a larger African security force slowed by delays and kit shortages, there are fears the Islamist jihadists will hit back with more guerrilla raids and suicide bombings.
Malian army officers said the north Gao checkpoint came under attack late on Saturday by a group of Islamist rebels who fired from a road and bridge that lead north through the desert scrub by the Niger River to Bourem, 80 km (50 miles) away.
"Our soldiers came under heavy gunfire from jihadists from the bridge ... At the same time, another one flanked round and jumped over the wall. He was able to set off his suicide belt," Malian Captain Sidiki Diarra told reporters.
Besides the bomber, who was blown to pieces, one Malian soldier was lightly wounded, Diarra added. In Friday's motorbike suicide bomber attack, a Malian soldier was also injured.
Diarra described Saturday's bomber as a "bearded Arab". Soldiers had collected body parts in a wheelbarrow and the bearded head of a light-skinned man was visible among them.
French military sappers carried out three controlled blasts in the area to destoy other devices and munitions found.
Since Gao and the UNESCO World Heritage city of Timbuktu were retaken last month, several Malian soldiers have been killed in landmine explosions on a main road leading north.
French and Malian officers say pockets of rebels are still in the bush and desert between the major towns and pose a threat of hit-and-run guerrilla raids and bomb attacks.
The French, who have around 4,000 troops backed by planes, helicopters and armoured vehicles deployed in Mali, are now focusing their offensive operations several hundred kilometres (miles) north of Gao in a hunt for the Islamist insurgents. (Additional reporting by Tiemoko Diallo and Adama Diarra in Bamako; Writing by Joe Bavier and Pascal Fletcher; Editing by Pascal Fletcher)