* Murder of French journalists highlights northern insecurity
* Al Qaeda-linked groups replace leaders
* Mali's president seeks support of ex-rebels in vote
By David Lewis and Laurent Prieur
DAKAR/NOUAKCHOTT, Nov 14 (Reuters) - Nine months after they were scattered across the Sahara by waves of French air strikes, Islamists in Mali are making a comeback - naming new leaders, attacking U.N. peacekeepers and killing two French journalists.
Their return is making it harder for the west African country's new president Ibrahim Boubacar Keita and his foreign backers to stabilise the northern desert despite the incentive of more than $3 billion in international aid for the area.
Mali imploded last year when Tuareg separatists tried to take control of the north. Their rebellion was soon hijacked by better-armed and funded Islamic militants linked to al Qaeda before the French intervention in January.
Increasingly blurred lines between the Islamist militants, separatist rebels and gangs of smugglers has complicated the task of calming the area and Keita's party has allied itself with leaders of some armed groups in a bid to wield influence.
Experts are starting to worry that France will get bogged down in an open ended war if U.N. peacekeepers cannot pick up the baton.
"Mali is entering a guerrilla war, waged by sleeper cells and fighters who returned from southern Algeria, Libya and Niger," said a French former diplomat and counter-terrorism expert who blogs under the name Abou Djaffar.
Last month, two Chadian U.N. troops were killed in a suicide attack in the remote town of Tessalit. Gao, the largest city in northern Mali, has been hit by a series of rocket attacks, while French special forces have taken action against Islamists north of Timbuktu for the first time in months.
But it was the killing of two French journalists, seized in broad daylight in the northern town of Kidal on Nov. 2, which sent shockwaves through France. Al Qaeda-linked fighters said the killings were a response to France's Mali operation although analysts say it may have been a botched kidnapping.
France dispatched reinforcements to Kidal after the journalists' deaths but insists it will not further delay its plan to reduce its 3,200 troops in Mali to 1,000 by February, already two months later than originally scheduled.
"We are conscious that it will take a long time to eradicate the terrorism threat in the Sahel (desert)," a French diplomat said.
"Of course, there is Serval (the French operation) and MINUSMA (the U.N. mission), but long-term efforts will be needed and a deep regional coordination to completely kill the terrorism threat in Mali."
Donors are once again disbursing aid after Keita's election in August restored a legitimate government. Military officers seized power in March 2012 in anger at President Amadou Toumani Toure's handling of the Tuareg rebellion.
Keita won power with a pledge to remove the web of corrupt elites that rotted the state under Toure. But with parliamentary elections on Nov. 24, Keita's party has allied itself with some leaders of armed groups who the previous government sought for war crimes.
"They are reverting to the same old practices," said Wolfram Lacher, an associate at the German Institute for International and Security Affairs. "The whole complex of drug trafficking, organised crime and warlordism is going to be back in place. I didn't expect it to happen quite so quickly and so openly."
FOREIGN FORCES STRETCHED
The journalists' killing highlighted the gaps in foreign military cover in a country twice the size of France. French troops in Kidal had to call in helicopters from Tessalit, 250 km (155 miles) away to try and track them down. France has just 16 in all of Mali.
Five months into its mandate, the U.N. mission is only at half strength. Regional military power Nigeria pulled its troops out and Mauritania, Mali's western neighbour with long experience fighting Islamists, has refused to join.
The bills are mounting at a time when Paris is under pressure to cut defence spending. According to a Senate report on the defence budget, the Mali operation will cost 650 million euros in 2013. Add the support for African allies and the final amount will be much higher.
Angering many in Bamako, France refused to carry out military operations against Tuareg separatist MNLA rebels in Kidal, saying the government should open a political dialogue.
A fusion of the MNLA with one Arab and one Tuareg group further blurs the line between rebels with a political agenda and Islamists. They are due to hold talks with the government about a solution to the problems in the north.
Under a June peace deal to allow presidential elections to go ahead, the three groups agreed to confine their troops to barracks. Many have not and in Kidal, where there is little army presence, gunmen slip in and out of the town, avoiding checkpoints along sandy tracks that fan out into the desert.
"Kidal is worse because the armed groups are no longer in control but the government is not in control either," said an official at the U.N. mission.
Underscoring these shifting alliances, the main suspect in the killing of the French journalists is linked to both the MNLA and AQIM.
The hit-and-run attacks by the Islamists mark a return to 'business as usual', said Yvan Guichaoua, Sahel expert at the University of East Anglia.
France's offensive killed hundreds of Islamists. Al Qaeda's North African wing, AQIM, was hardest hit, losing Abdelhamid Abou Zeid, its senior leader in the zone, and several other key figures. But the group has been busy restructuring.
Abou Said el-Djazairi, a fellow Algerian, replaced Abou Zeid as head of the Tarek Ibn Zyad brigade in northern Mali. El-Djazairi is a 40 year-old veteran of AQIM's Sahel operations, including the 2010 kidnapping of French mine workers from northern Niger, regional security sources said.
Mauritanian Abdarrahmane Al Liby, aka Talha, has replaced Abdallah Al Chinguetti, another of its killed commanders. Al Liby is close to Yahya Abou el-Hammam, AQIM's top Sahara commander, and is believed to have been part of a desert raid that killed 12 Mauritanian troops in 2008, the sources said.
Mokhtar Belmokhtar, a former AQIM chief who formed his own group, has joined forces with MUJWA, another AQIM splinter, to carry out attacks, including suicide bombings in Niger in May.
In the face of French firepower, many Islamists had sought safehaven outside Mali, especially in southern Libya, security experts said. However, many others just kept their heads down.
"They have always been there but they were just observing," said an international security source who monitors northern Mali. "We are seeing a resurgence in activity."
The violence suggests Islamists won local recruits during their occupation but are now also using suicide bombings, a new tactic from AQIM's North African operations, Guichaoua said.
Timbuktu residents say they fear venturing outside town. The French diplomat said Paris was under no illusion the threat had been eradicated: "They are waiting for the storm to pass and then they will try to rebuild their capacities progressively."
OLD HABITS DIE HARD
Analysts say that Malian and French political leaders are repeating mistakes partly to blame for Mali's implosion.
Security experts say they are convinced France once again paid a multi-million dollar ransom to secure the release last month of four French citizens kidnapped three years ago. French media, citing French intelligence sources, have also said a ransom was paid.
Paris, which denied any payment, had pledged an end to such payments that netted Islamists tens of millions before the war.
"This is another example of French incoherence: shifting between tough posturing and secret compromises to save lives," said Abou Djaffar.
Bamako has also attracted criticism for its compromises.
In the name of reconciliation, it lifted the arrest warrants for four key rebel figures. Two of them, Ahmada Ag Bibi and Mohamed Ag Intallah, were named to the electoral list of Keita's party to bolster its support with northern elites.
Lacher said the men were not extremists but opportunists who joined armed groups to strengthen their position. Nonetheless, the deal would discredit Keita's pledge to end injustice, he said: "It's not a question of extremism but impunity."
In Gao and Timbuktu, where residents are proud to have resisted occupation by Tuareg rebels and then the Islamists, the alliances Bamako is forging are deeply unpopular.
"These are people who took up arms against Mali and killed civilians," said Amadou Sarr, leader of a local militia during the occupation. "They're going back to their old habits and we are not ready to accept this." (Additional reporting by Adama Diarra in Timbuktu and John Irish and Patrick Vignal in Paris; editing by Anna Willard)