* PM Mara says Islamists fighting alongside separatists
* Sees obstacles to negotiation with armed groups
* Tuareg groups meet in Algeria
By Joe Penney
BAMAKO, June 10 (Reuters) - The international community is underestimating the threat posed by Islamist fighters sheltering in areas of Mali's far north controlled by Tuareg separatist rebels, Prime Minister Moussa Mara said.
When Mara travelled to the Tuareg stronghold of Kidal last month, clashes broke out between rebel groups there and troops.
Mali's army launched an operation to seize Kidal but was defeated by the rebels, who seized more towns. The fighting threatened to wreck fragile peace negotiations and plunge the country back into war.
Mara told Reuters in an interview on Monday that the armed groups who seized Kidal last month had jihadist elements within them which posed a threat to the peace of the region.
"The international community is not giving the importance needed to the jihadist threat in Kidal," Mara said in his office overlooking the Niger river in the dusty capital, Bamako.
"At the moment, there are jihadists in Kidal. They arrived even before I got there."
Mali was thrown into chaos in 2012 after a Tuareg uprising was hijacked by better-armed Islamist groups linked to al Qaeda's north African wing (AQIM). Taking advantage of a coup in the capital, they seized control of Mali's vast desert north.
France, saying the enclave posed a threat to western security, led a military intervention last year that scattered the Islamists. Armed Tuareg separatists were allowed to retain control of Kidal, irking President Ibrahim Boubacar Keita.
The separatist movements demand greater autonomy for north Mali, which they term Azawad. The three main groups - the National Movement for the Liberation of Azawad (MNLA), the Arab Movement of Azawad, (MMA) and the High Council for the Unity of Azawad (HCUA) - have denied having links with Islamists.
Mara said the Islamists would dominate the separatists as they did in 2012. "For the jihadists, breakfast will be the MNLA. Lunch will be Mali. And dinner will be the West," he said.
NO TERRITORY FOR ISLAMISTS
After a five-day meeting in the Algerian capital, the three separatist groups on Monday signed a declaration agreeing to stand by a May 23 ceasefire brokered by the African Union and the United Nations following the fighting in Kidal.
They also agreed to pursue negotiations with the Malian government under the auspices of an external mediator at a date and place to be agreed with Bamako, according to the statement.
France welcomed the Algiers declaration as a step towards a peace deal that would respect Mali's territorial integrity, and urged the government to start negotiations quickly.
But Mara said the presence of jihadists within the separatist groups threatened any peace talks because his government could not cede territory to Islamists.
"Say we give the Kidal region more resources and a lot more decentralized power, and they elect a jihadist to lead Kidal. That means we would have given our territory to jihadists, and democratically. This is what we want to avoid," he added.
One of the obstacles for peace, according to Mara, is that there are no clear borders between the groups, with Islamist fighters drifting into separatist movements when it suits their political and military objectives.
"They have the same interests when their adversary is the Malian army. It's when they are left to their own devices that the differences appear," Mara said. (Reporting by John Irish in Paris and Emma Farge in Dakar; Writing by Bate Felix; Editing by Daniel Flynn and Andrew Roche)