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Guerrillas of the Revolutionary Armed Forces Colombia (FARC) are concealing vital components of their arsenal, according to intelligence analysts, including sophisticated anti-aircraft missiles they agreed to surrender in a peace deal signed with the Colombian government last year.

In the agreement, FARC committed to turn over its stocks of weapons and explosives within the first six months of 2017 in exchange for immunity from prosecution, political representation in Congress and other concessions from the government.

So many in the country believe the deal was overgenerous with the FARC that a slim majority voted against its approval in a national referendum last November.

But four months into the agreement’s implementation, the rebel army – believed to number around 7,000 fighters by the latest official estimates – has handed in less than 1,700 rifles to U.N. peacekeepers, according to Colombian officials.

Furthermore, U.S. and Colombian intelligence analysts contend FARC leaders are refusing to disclose details about the quantity and type of the armament. Spokesmen for the rebel group have mentioned 7,000 rifles — more or less equivalent to one rifle per demobilized fighter.

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President Juan Manuel Santos has said that he expects the group will turn in 14,000 rifles. But ambassador to Washington and former Defense Minister Juan Pinzon says that he knows of no current official estimates as to the size of FARC's arsenal.

FARC chairman Ivan Marquez has said it is “secret.”

“They don’t talk about a single missile, although we know that they have Russian SAMs acquired through the international black market,” said Jose Marulanda, a Colombian army intelligence officer and international security consultant, to Fox News.

According to Marulanda, there is so little control over the disarmament process that U.N. supervisors have not even registered the serial numbers of the few weapons turned in.

When the U.S. stepped up its military aid to Colombia in 2000, FARC mounted a major international effort to acquire shoulder-fired SAMs to counter U.S.-supplied Blackhawk helicopters that enabled the Colombian military to reach the rebels’ remote jungle hideouts.

The ensuing standoff between the government and the rebel group was a factor that brought them to the negotiating table.  

But FARC continued its search for new weapons. Even while talks were in progress, intelligence documents obtained by Fox News show the group purchased $88,585,000 worth of weapons from Russia arms dealers.

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The most recently weapons acquired by FARC allegedly include 200 portable surface-to-air missiles, according to documents extracted from the computer of a guerrilla commander killed in an army raid in July 2013.

An inventory of the alleged weapons purchase includes orders for 150 Igla SA-18 shoulder-fired missiles, whose sensitive infrared homing system and resistance to flares enable them to shoot down straight winged aircraft; 50 older model SA-7s and 500 Konkurs ATGM anti-tank missiles.

FARC also ordered about 2,000 PKM, DSHK and NSV heavy machine guns, 12,000 AK-47 and AKM-74 automatic rifles, 3000 AK 74-U submachine guns, 1,000 Dragunov and OSV-96 sniper rifles, 300 Tokarev pistols and over five million rounds of ammunition, according to the dead leader’s files.

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Colombian and U.S. defense officials confirmed to Fox News the authenticity of the intelligence documents but said that they have not traced the trajectory or location of the weapons.

A Colombian military official who acted as an advisor to the government negotiating team at the four-year peace talks in Cuba, said that the weapons were shipped through Venezuela to FARC camps in the border zone of Catatumbo.

A U.S. defense department terrorism analyst, who requested to remain anonymous, said that most of the arms are probably stored in Venezuela, whose security services allegedly have ties with FARC.

FARC has maintained a constant flow of weapons over decades, financed with billions of dollars from drug traffic, kidnapping, extortion and other illegal ventures. Colombian and U.S. intelligence sources believe that the group may have accumulated one of the world’s biggest terrorist arsenals, with about 40,000 arms.

Sixty thousand AK-47 rifles were delivered to the group in just one smuggling operation in 1999 assisted by Peru’s corrupt ex security advisor Vladimiro Montesinos, who is currently in prison.

FARC has been such a steady customer of international arms dealers that undercover FBI agents posing as buyers for the group mounted a sting operation that resulted in the arrest of notorious Russian arms dealer Victor Bout, immortalized in the Hollywood movie “Lord of War.”

Some analysts fear that FARC’s excess armory may get recycled into the international black market, feeding a growing network of terrorist groups and criminal gangs throughout Latin America.

The Wall Street Journal recently reported that rogue FARC members have offered their services to drug trafficking gangs fighting for control of Brazil’s big city favelas.

According to the peace agreement, FARC is allowed to keep some weapons to arm a security service for its leaders, who are now planning to enter politics.

Martin Arostegui has covered Latin America for the Washington Times, the Wall Street Journal and other news organizations. He is the author of "Twilight Warriors" (St Martin's), a book on counterterrorism.