The UN Security Council on Monday decided to establish a new mission in Colombia to help FARC (Revolutionary Armed Forces of Colombia) rebels reintegrate into society as the peace deal moves to a challenging phase after the laying down of weapons.

After the historic agreement ended half a century of guerrilla war, the FARC completed the handover of individual weapons on June 27, under UN supervision.

The council unanimously adopted a British-drafted resolution that sets up the new verification mission as of September 26, when the first mission overseeing the disarmament ends.

The UK and the United States stressed that this new phase, when 10,000 rebels are to begin new lives as civilians, is shaping up as a crucial test for the peace deal reached last year.

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"Experience from our own history in Northern Ireland has taught us that the hardest part remains ahead," British diplomat Stephen Hickey told the council.

"A sustainable and lasting peace will depend on the FARC's successful reincorporation into civilian life."

US Deputy Ambassador Michele Sison said the peace deal was entering a "critical next phase" and stressed the importance of rural development and counter-narcotics.

For decades, the FARC controlled areas where coca leaf and cocaine production flourished, but now farmers in those areas will be given incentives to turn to other forms of agriculture.

The rebel group will also set up a political party while thousands of combatants currently in jail will receive amnesty.

France is providing a package of aid and loans of 820 million euros ($930m) to support the peace process, Ambassador Francois Delattre said.

The council asked UN Secretary-General Antonio Guterres to provide a report to the council in August on preparations for the new 12-month mission including details on its size and mandate.

Addressing the council, Colombian Foreign Minister Maria Angela Holguin acknowledged that bringing peace and prosperity to the FARC's former strongholds in the countryside is "our main challenge."

"The development of political participation, greater equity and better justice will be fundamental to become the country that we want to be," she said.

In the coming two months, the FARC will finish handing over weapons stashed in arms caches, completing the disarmament process, the foreign minister said.

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UN envoy Jean Arnault told the council last month that the FARC were struggling with "a deep sense of uncertainty" over their physical safety and their future after the disarming.

Ensuring that the former combatants can join mainstream society is the "first and most urgent challenge" in Colombia, he stressed.

Colombian President Juan Manuel Santos was awarded the Nobel Peace Prize for reaching the historic deal with the FARC, ending more than 50 years of conflict with the group that has left 260,000 dead.

About 60,000 Colombians remain unaccounted for and seven million were displaced in the conflict.

The government has been holding talks with the last active guerrilla group, the National Liberation Army (ELN), in Ecuador where the chief negotiator for the rebels, Pablo Beltran, told AFP news agency last week that a ceasefire is near.