* Attack targeted same Gao checkpoint that was hit on Friday
* French troops reinforce position with armoured vehicles
* Bands of Islamist insurgents reported still around Gao
* As French hunt in mountains, fears of guerrilla war emerge (Recasts, adds details, quotes from Malian officer, resident)
Malian troops foiled a second suicide bomber attack in the northern town of Gao late on Saturday, highlighting fragile security in zones recaptured by a French-led offensive that is hunting Islamist insurgent bases further north.
French forces rushed reinforcements and armoured vehicles on Sunday to the Malian army checkpoint on Gao's northern outskirts which was the same location attacked by another suicide bomber on a motorcycle on Friday.
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", saying this had been visible from the body parts collected by the soldiers in a wheelbarrow.
"We heard shooting at around 11 p.m. and closed our doors, and then there was an explosion ... In the morning we found that someone had blown up and part of his body landed here," said Abderaman Idrissa, who lives in a mud home near the checkpoint.
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.
"ISLAMISTS IN THE AREA"
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.
"There are Islamists in the area," Diarra said, adding that French air strikes late on Saturday destroyed three rebel vehicles, out of about 20 spotted moving in the countryside.
"We are in a dangerous zone, the enemy is employing asymmetrical tactics ... we can't be everywhere," a French officer told reporters, asking not to be named.
One local resident reported seeing a group of 10 armed Islamist fighters at Batel, just 10 km (6 miles) from Gao.
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.
On Friday, French special forces paratroopers seized the airstrip and town of Tessalit, near the Algerian border.
From here, the French, who are backed by around 1,000 Chadian troops in the northeast Kidal region, are expected to conduct combat patrols into the Adrar des Ifoghas mountains.
In this rugged, sun-blasted range of rocky gullies and caves, the remaining Islamists are believed to have hideouts and supply depots and are also thought to be holding at least seven French hostages previously seized in the Sahel.
The United States and European governments are backing the French-led operation in Mali as a defence against Islamist jihadists threatening wider attacks, but they have ruled sending their own ground combat troops.
To accompany the military offensive, France and its allies are urging Mali's authorities to open a national reconciliation dialogue that addresses the pro-autonomy grievances of northern communities like the Tuaregs, and to hold democratic elections.
Mali's interim President Dioncounda Traore, appointed after last year's military coup that plunged the West African state into chaos and led to the Islamist occupation of the north, has said he intends to hold elections by July 31.
But he faces splits within the divided Malian army, where rival units are still at loggerheads.