United Nations soldiers will take over from African troops in conflict-scarred Mali from Monday, making up the organisation's third-largest peacekeeping force by the end of the year.

A 12,600-strong force will take over security duties from French troops who entered Mali in January to halt an Islamist advance and help the government re-establish its authority over the vast country.

France is winding down its deployment from its peak of nearly 4,500 but is to keep up to 1,000 troops in Mali and they will maintain responsibility for military strikes against the Islamists.

"Security conditions are satisfactory, no major attack has been recorded against the Malian and African forces, and most important, despite what certain people feared, the political process has experienced a very positive evolution," France's UN ambassador Gerard Araud said, welcoming the handover.

Rwandan General Jean-Bosco Kazura, formerly second in command of African Union troops in Sudan's western Darfur region, will lead the force.

The majority of his soldiers will be Africans already stationed in Mali but China has offered to supply more than 500 troops in what would be its biggest contribution to UN peacekeeping.

Sweden will send around 70 troops for a maximum of one year while Norway is to contribute 25 soldiers and police.

Bangladesh is thought to have offered the largest non-African contingent of up to 1,000 troops although no deal has yet been confirmed.

UN leader Ban Ki-moon has raised fears that the peacekeepers could face guerrilla attacks and has highlighted the lack of equipment and training among the West African troops already in Mali.

Armed militias "retain the capability to pose a significant threat" and "still have support networks and recruitment structures in place", Ban said in a report published on June 9.

The UN mission is due to play a key role in presidential polls announced for July 28 but the election commission has raised doubts over its ability to stage a free and fair vote with such short notice.

A total of 36 candidates have applied to stand in the election, including two women and four former prime ministers, Mali's constitutional court said Saturday.

The commission's president Mamadou Diamountani said this week it would be "extremely difficult" to get up to eight million voting cards to the electorate in a country where 500,000 people have been displaced by conflict.

He also highlighted the instability in the northeastern town of Kidal, which is occupied by Tuareg separatists and still has no army presence despite a ceasefire between the transitional government and the rebels.

But Tuaregs from the National Movement for the Liberation of Azawad (MNLA) in Kidal said Saturday that "nothing justified delaying" the poll.

In a written statement, they said a delay "would have a prejudicial impact on the implementation of the accord by the agreed deadline", referring to a deal signed in Burkina Faso envisaging a ceasefire between the Malian army and the Tuaregs during the election period.

That accord also outlines peace talks for after the vote.

Malian military officers staged a coup in March last year, but the weak army was overpowered by the MNLA front which seized key northern cities before being sidelined by its Al Qaeda-linked allies.

The MNLA sided with a French-led military intervention which reclaimed most of the lost territory from the Islamists.

The UN has called on member states to contribute critical resources to ensure that it can support Mali in implementing the Burkina accord and preparing for the elections.

"We count on the continued support of both our traditional and new troop-contributing countries to help us fill these critical shortfalls," said Under-Secretary-General for Peacekeeping Herve Ladsous.

Beyond the threat of armed insurgents, the "blue helmets" will also find the challenge of the harsh terrain in arid northern Mali, where the temperature regularly reaches 48C (120F) and where water is scarce.

"All information and communications technology, vehicles, refrigeration, and tentage that is ultimately used in Mali will be exposed to climatic conditions that accelerate their decay," Under-Secretary-General for Field Support Ameerah Haq told the council.

Haq called it "one of the most logistically challenging missions the United Nations has ever launched" but said planning was on track.