Fighting triggered by a rebel assault on Chad's capital N'Djamena last month killed some 700 people, President Idriss Deby said in comments broadcast on Thursday.

Deby had said 400 civilians were killed in N'Djamena during the fighting a month ago. He told French television station France 24 the new figure included soldiers and those killed in the nearby town of Massaguet.

"The total death toll is around 700 including N'Djamena and Massaguet, the town some 80 km east of N'Djamena. Those were the two martyrs' towns," he said, according to an advance copy of the interview.

Rebels opposed to Deby attacked N'Djamena on February 2 and besieged his presidential palace. Government forces pushed the insurgents back after two days of heavy fighting.

Deby has fought off several rebel bids to end his 18-year rule in the central African oil producer and has repeatedly blamed the president of neighbouring Sudan, Omar Hassan al-Bashir, for backing the rebel offensives.

Deby, interviewed in his palace in N'Djamena, said he believed Khartoum was re-arming the rebels for another attack.

"It is not impossible, and I will even confirm that Sudan is equipping those (insurgents) who left here with new weapons, new means to prepare for attacks," Deby said.

"It's not the rebellion that wants to overthrow President Deby. On the contrary, it's Sudan that wants to install a regime devoted to it so it can propagate in sub-Saharan Africa a form of Islamism, because the system in Sudan is pure Islamism."

Deby said he had not yet decided whether to pardon six French aid workers jailed for eight years for trying to fly 103 African children to Europe without permission.

The members of charity Zoe's Ark were jailed in Chad in December but later transferred to a French prison. Their lawyers last month requested a presidential pardon from Deby.

"We have not yet decided ... We have judicial procedures here," Deby said. If due process were followed, he would in theory be prepared to issue a pardon, he said.

But he wanted to know who would pay the 4 billion CFA (4.6 million pounds) compensation he said the families of the children were owed for the ordeal they had been through.

"Will it be France? Will it be members of Zoe's Ark? ... With the exchanges that we will have with the families and with France, we will find a solution which will clearly allow the six members of Zoe's Ark to widen their freedom," he said.