Rockets were fired on northern Mali's largest city of Gao Thursday, days before legislative elections are to be held in the troubled west African nation, security sources said.

The first shot was heard around 5:00 am (0500 GMT), a security source in Gao said, adding that it was "a powerful shot, which made a lot of noise but left no damage".

Islamists fired shells on Wednesday towards airport in Gao, Mali's second-largest city, but did not cause any casualties, a source from the Malian army headquarters said.

"The Islamists fired shells towards the airport in Gao" where French and Malian soldiers are stationed, the source said.

A rebel group seeking independence in northern Mali said on Thursday it had appointed an "administrator" to Kidal in a show of strength after French-led troops liberated the town from an Islamist occupation.

The Tuareg National Movement for the Liberation of the Azawad (MNLA) told Agence France Presse that Mohamed Ali Ag Albessaty, previously a local government functionary, would serve as its top official for Kidal.

Clashes between the Malian army and Islamists killed seven people Sunday, including a soldier and two civilians, military sources said, after militants infiltrated northern Mali's largest city, Gao.

The fighting took place as the Malian army carried out what it called a "clean-up" operation after Islamist militants opened fire on an army camp in Gao overnight.

Thousands of people who fled when Islamists attacked the largest city in Mali's war-torn north have returned, a survey by a local charity working to resettle refugees told Agence France Presse on Thursday.

Tassaght said a study of returning refugees and internally displaced people indicated that 5,800 residents who fled the occupation by al-Qaida-linked Islamists had come home, most after Gao was liberated in late January.

At least 50 Al-Qaida-linked rebel fighters have been killed in recent days in clashes with French and Malian troops near the town of Gao in northern Mali, a Malian military source told AFP on Sunday.

"Fighting continues on Sunday morning some 60 kilometers (37 miles) north of Gao between Islamists and Malian troops supported by the French army. We have the situation under control," said a Malian military source contacted by phone from the capital Bamako.

Islamists in northern Mali have the "destructive power" of an army, a top Malian colonel said Sunday, while showcasing weapons seized in Gao since French-led forces retook the city last month.

"What we have here, it's indicative of an army, or groups that have the capacity of an army," said Gao commander Laurent Mariko, showing the stockpile of weapons to reporters.

One of the main Islamist armed groups in northern Mali said Thursday it had sent fighters back into Gao, a city it controlled for nine months before French and Malian troops recaptured it last month.

"Our fighters entered Gao on Wednesday," Abu Walid Sahraoui, a spokesman for the Movement for Oneness and Jihad in West Africa (MUJAO) told Agence France Presse.

Malian troops were battling armed Islamists in the northern city of Gao on Thursday in clashes that left the main courthouse in flames, an Agence France Presse correspondent and a military source said.

Fighting had first erupted overnight in Gao, where a military official and witnesses reported heavy gunfire around two main entrances to the main city in the north of the country.

Boncana Amadou, the 93-year-old chief of the village of Kadji in northern Mali, points a worn finger toward the Niger river and a strip of land down the middle that locals call "Fundamentalist Island".

"Do you see that there?" Amadou says. "Those are Malian fundamentalists living there, and they've been sheltering Islamists from MUJAO."