UNITED NATIONS — The U.N. Security Council approved the July 1 deployment of a Mali peacekeeping force tasked with helping the government regain control of rebel-held areas and organize crucial elections, all while facing harsh challenges in a vast desert territory.

A June 18 accord between Mali's government and the Tuareg rebels has raised hopes that the West African country is on track to regaining stability after losing half its territory last year to a rebel invasion.

The 15-country Security Council unanimously decided that conditions are in place to start deploying the peacekeeping mission on July 1 as scheduled, Britain's U.N. Ambassador Mark Lyall Grant told reporters after a council meeting. The 12,640-member U.N. force will replace a 6,000-member African-led mission now in Mali.

Some of the French troops who ousted radical Islamic groups from northern Mali in January will remain in the country, ready to intervene under a soon-to-be signed agreement if the U.N. mission comes under "imminent and serious threat," said Herve Ladsous, the U.N. undersecretary-general for peacekeeping operations.

French Ambassador Gerard Araud said some of the 3,000 French troops now in the country will begin withdrawing at the end of the summer with the aim of reducing the force to 1,200 by the end of 2013.

The Tuareg rebel force seized the major northern cities of Timbuktu, Gao and Kidal last year. But on their coattails came a trio of al-Qaida-aligned armed groups that within weeks seized much of northern Mali. In January, France scrambled fighter jets over Mali to beat the Islamic radicals back. The Malian army quickly returned to Timbuktu and Gao, but the Tuareg separatists have retaken Kidal and established a shadow administration.

The immediate challenge for the new U.N. force will be to help implement the agreement with the separatists in Kidal, including disarming the rebels and accompanying the return of the Malian army to the city. That is crucial to the success of presidential elections scheduled for July 28, said Albert Gerard Koenders, the secretary-general's special representative for Mali.

The U.N. mission will play a key support role in the election, including distributing of identification cards to voters in the north, many of them displaced by the fighting, Koenders told the council.

The extreme heat in northern Mali has made the U.N. force "one of the most logistically challenging missions the United Nations has ever launched," said Ameerah Haq, the U.N. undersecretary-general for field support.

An engineering assessment team has determined that the mission cannot tap into Kidal's reservoirs without jeopardizing the local water supply. Haq told the council that means the United Nations must look into other technologies to produce water from air humidity.

The U.N. force will comprise the majority of troops from the African mission already there, who have four months to meet U.N. human rights and equipment standards.

Those include Chadian troops who helped the French fight the Islamists in January, their experience in desert terrain proving crucial. Human rights groups have objected to the inclusion of the Chadian military in the new force because it is on a U.N. "list of shame" of child recruiters. Ladsous said the U.N. "is making every effort to screen the Chadian contingent to ... ensure that no troops under 18 are among them."