ROUGH CUT (NO REPORTER NARRATION) STORY: French and Malian troops fought Islamists on the streets of Gao, as fighting showed little sign of abating weeks before France plans to start withdrawing some forces. Reuters reporters in Gao in the country's desert north said French and Malian forces fired at the mayor's office with heavy machine-guns after Islamists were reported to have infiltrated the Niger River town during a night of explosions and gunfire. French troops dispatched to root out rebels with links to al Qaeda swiftly retook northern towns last month. But they now risk being bogged down in a guerrilla conflict as they try to help Mali's weak army counter bombings and raids. Gao is a French hub for operations in the Kidal region, about 190 miles or 300 kilometers northeast, where many Islamist leaders are thought to have retreated and foreign hostages may be held. French troops in armored vehicles later joined the battle as it spilled out into the warren of sandy streets, where, two weeks ago, they also fought for hours against Islamists who had infiltrated the town via the nearby river. Paris has said it plans to start withdrawing some of its 4,000 troops from Mali next month. But Mali's army remains weak and divided and African forces due to take over the French role are not yet in place. Islamists abandoned the main towns they held but French and Malian forces have said there are pockets of Islamist resistance across the north, which is about the size of France.