UNITED NATIONS (AP) — The U.N. Security Council on Thursday unanimously approved U.N. plans for a follow-on mission in Colombia which will focus on reintegrating some 10,000 former combatants from the country's largest rebel group back into society.

A resolution adopted by the council welcomes the laying down of arms by the Revolutionary Armed Forces of Colombia, or FARC, after more than 50 years of war, a process monitored by the United Nations.

Britain's U.N. Ambassador Matthew Rycroft called the new U.N. mission "an important step" to consolidate gains over the past year and move to "the next crucial phase."

While Colombian President Juan Manuel Santos has said implementation of the peace agreement with the FARC was irreversible, Rycroft stressed that "irreversible and sustainable are not exactly the same."

"We have officially reached the hard bit now," Rycroft said.

Handing over weapons took "a moment," he said, but re-incorporating FARC combatants into society will require commitment and sacrifice and "will mean putting aside difference that were born long before most Colombians."

Rycroft stressed that "sustainable peace will depend on the FARC's successful reincorporation into public life."

U.S. deputy ambassador Michele Sison said "Colombia has shown the world that commitment for a political process and a shared future along with strong, unified support from the council and the international community can bring success in peace-building."

"Now Colombia faces the challenge of consolidating that peace," she told the council. "The threat to that peace is serious and comes in the form of lack of infrastructure, basic services and rule of law in conflict-affected areas formerly occupied by the FARC, creating a haven for criminal activity, drugs and violence."

Sison said the Security Council remains committed to creating conditions for peace.

Jean Arnault, the U.N. envoy for Colombia, briefed the council Monday and outlined steps the U.N. mission has taken to start the new U.N. verification mission on time on Sept. 17, when the mandate of the current mission monitoring the cease-fire and disarmament process ends.

The Security Council also welcomed the Colombian government's announcement that the country's last remaining rebel group, the National Liberation Army, or ELN, will observe a temporary cease-fire from Oct. 1 until Jan. 12, 2018.

Rycroft told the council after the vote "it's also very encouraging that the parties have indicated that they would like the U.N. to play a role in verifying that cease-fire."

"We stand ready to support in whatever way we can," he said, adding that the Security Council was waiting for advice from Secretary-General Antonio Guterres.

Earlier, Rycroft told reporters that all 15 council members want to help Colombia oversee "this very important cease-fire" with the ELN and there are "a number of different ways that the request can be acceded to." He said he expects a decision "sooner rather than later, but we are taking our time to make sure that everyone is happy."