Strong resistance by Moamer Kadhafi's forces and conflicting impulses to topple the Libyan ruler and hit a political settlement are stumping France's and its allies' efforts to end the conflict, experts say.

French Foreign Minister Alain Juppe has denied France is getting sucked into an endless war but admitted "we probably underestimated the resistance that would be put up by Kadhafi's forces," in televised comments on Thursday.

"We cannot speak of getting bogged down," he insisted. "We are five months into our operations... no one talked about a lightning war."

The Western coalition behind the bombings of Kadhafi's military assets, coordinated by NATO and mostly waged by France and Britain, launched its campaign under a UN mandate to protect civilians from a violent crackdown.

The allies soon added calls for Kadhafi to quit power.

"The international community wants Kadhafi to go," said Jean-Yves Moisseron of the IRD research institute. "But with the current distribution of forces and control of the territory, there can be no political solution without Kadhafi," he added.

"There is therefore no way out. They are bogged down for some time and it is not certain that Kadhafi will leave because the international community and France in particular does not have the means for a long war."

France's Defence Minister Gerard Longuet said Thursday the French aircraft carrier Charles de Gaulle would come home from the Libya mission for maintenance next week, but insisted the French airstrikes would continue.

The French navy's website said Thursday it would take "several months" to complete work on the ship that has been engaged in the operation since March 22.

Italy has pulled out an aircraft carrier from the NATO-led Libya mission and Norway on Monday withdrew the last of its fighter-bomber jets. Britain made up for this by adding four Tornado jets.

France and Britain last month softened their earlier line on Kadhafi, whose departure from Libya they had demanded, saying that he could stay in Libya if he gave up power under a negotiated settlement.

Sources have claimed there has been contact between the coalition, Kadhafi's regime and the rebel council, whose representatives have also met with French President Nicolas Sarkozy, but there is still no sign of a breakthrough.

Longuet said France was committed to striking Kadhafi's military assets for as long as needed for him to quit power and called on Libyans in Tripoli to rise against him.

Juppe said the rebel National Transitional Council's ground forces were "making progress in the south and the west of the country" and international forces would "continue to put this military pressure" on Kadhafi.

The rebels on Friday said a NATO strike had killed Moamer Kadhafi's youngest son Khamis and 31 others, a claim denied by the authorities in Tripoli.

But observers played down the rebels' advances and said tribal divisions in Libya make it difficult to coordinate an uprising, especially during the current Muslim fasting month of Ramadan.

"Libyans are willing to fight for their land but when it comes to waging war on other (tribes') territory it's a different matter," said Patrick Haimzadeh, a former diplomat and author of a book on Kadhafi's regime.

Moisseron of the IRD added that Kadhafi himself has been allied from the start with certain powerful tribes while, for example, "the Berber tribes of Jebel Nefusa are ready to defend their territory but will not go to Tripoli."

Questions are meanwhile arising in France over the legitimacy of the military campaign. One senior member of parliament, Jean-Jacques Candelier of the Communist party, called for a commission to be set up to examine its aims.