BOGOTA (Reuters) - Police seized more than 12 tons of cocaine from Colombia’s top crime gang on Wednesday, the biggest haul ever in the nation’s long-running fight against drug trafficking, President Juan Manuel Santos said.

The cocaine, with a U.S. market value estimated by Santos at about of $360 million, was found stored underground on four farms in a banana-growing region of northwest Antioquia province, near Colombia’s border with Panama.

“Thanks to a police operation with overseas intelligence, from friendly countries, the largest seizure in history was made,” Santos said at a police base where the cocaine was laid out in packages on display.

Santos linked the cocaine to the drug-trafficking gang known as the Gulf Clan, which has become one of the biggest threats to security since peace was signed last year with Marxist-led Revolutionary Armed Forces of Colombia (FARC) guerrillas.

The seizure comes as the United States, Colombia’s staunchest ally in the fight against drug trafficking, has raised concern over an increase in coca cultivation and as the government faces criticism from opposition lawmakers for allowing new crime gangs to fill the void left by the FARC.

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Santos, who leaves office next year, has pledged to send 80,000 military and police to areas once controlled by the FARC in a bid to prevent new trafficking gangs from taking hold.

Four people were arrested during the three-day operation leading to the drug seizure, according to a police statement.

The Gulf Clan is led by fugitive Dairo Antonio Usuga, known as Otoniel. The United States has offered a reward of up to $5 million for information leading to his capture or death.

In addition to drugs, the gang deals in illegal mining and most if its estimated 1,500 members formerly served in the ranks of right-wing paramilitary groups.

Colombia is one of the world’s leading producers of cocaine, with output of around 910 tons per year, according to the U.S. Drug Enforcement Administration. Anti-drug police have confiscated 362 tons of cocaine this year.