Bogota pushed Friday for the United Nations to supervise Colombia's ceasefire with the FARC rebels, even before the country votes on a peace deal to end the long-running civil war.

The government and the country's biggest rebel force, the Revolutionary Armed Forces of Colombia (FARC), laid the groundwork for a full peace deal when they signed a definitive ceasefire in June.

That deal will be followed by a full peace accord only if the agreement is approved in a referendum in the coming months.

"We need the mission to deploy as quickly as possible," Sergio Jaramillo, Colombia's high commissioner for peace, told reporters.

Jaramillo said that when the referendum is held, the ceasefire mission should be already on the ground, giving "guarantees to Colombians that they can vote freely."

The first group of observers, of which there will eventually be 450, primarily from Latin America, has arrived in Colombia to verify the disarmament and monitor the ceasefire.

"From what I understand, at the latest in three or four weeks they should be able to be there in full force," Jaramillo said.

Their recruitment "took a bit of time to get going but now the numbers seem to be there," he added.

After the UN's onsite visit last week, the international organization and Bogota "have a much better idea of what happens on the ground," Jaramillo said

UN Secretary-General Ban Ki-moon on Friday delivered a report on the practical technicalities of the mission to the Security Council, which is expected to discuss it on August 26.

Ban confirmed that the UN mission will have about 450 observers, in addition to some civilian staff.

The mission will operate in 40 "widely dispersed locations," he said.

The ceasefire will be monitored by a three-party body manned by the government, FARC and the UN.

Ban's report highlighted the "positive reaction of the civilian population" and said conditions "show that preparations are on track not only from a technical viewpoint but also from a political perspective."

But he pointed out that only 80 observers had been recruited.

"Important issues remain on the table" in Havana, where the talks were held, the UN chief said.

The sustainability of the peace agreement depends on "the implementation of a reliable program of reintegration of the FARC-EP combatants," he said.

The government and the Marxist rebels are still in the final phase of four years of peace talks aimed at ending more than half a century of conflict.

The two sides signed a ceasefire and disarmament deal on June 23, with the guerrillas aiming to become a political party.

The territorial conflict began in 1964 and is the longest-running war in Latin America, having left at least 260,000 people dead, 45,000 missing and 6.8 million displaced.

FARC will begin to call in their troops for disarmament once the final peace accord is signed, which is seen as likely in the coming weeks.