Record cocaine busts in Guinea-Bissau and Cape Verde have fueled fears of a resurgence of drug trafficking in West Africa that’s likely to benefit Islamist militant groups in the region.

Authorities in the two former Portuguese colonies have intercepted as much as 10.4 metric tons of cocaine this year, more than the total amount seized on the entire continent between 2013 and 2016, according to the latest data available from the United Nations Office on Drugs and Crime.

Analysts say that gangs smuggling drugs into Europe pay Islamist militants linked to al-Qaida and ISIS to protect shipments crossing the Sahel and then the Sahara, even though the extent of the trade isn’t clear.

“There were doubts whether West Africa was still being used as a major transit route, but these seizures seem to suggest that there is a return,” said Mark Shaw, director of the Geneva-based Global Initiative against Transnational Organized Crime. “It’s a surprise and it’s very significant.”

On March 9, Guinea-Bissau recorded its biggest cocaine bust yet after discovering almost 1,764 pounds of the narcotic in a fish truck bound for Mali. Four people were arrested, including an adviser to the speaker of Niger’s national assembly who’s suspected of working for a businessman with links to al-Qaida in the Islamic Maghreb, known by its acronym AQIM, according to Domingos Correia, deputy national director of the judicial police.

“There are strong indications the shipment was connected to AQIM financing,” said Correia. “This marks a significant return of traffickers, and that is very concerning.”

Nearby, authorities in the archipelago of Cape Verde found 9.6 tons of cocaine on a Panama-flagged vessel, one of the biggest drug seizures ever outside top producer Colombia. The find has an estimated value of $720 million, or the equivalent of 41 percent of Cape Verde’s economy, according to United Nations and World Bank data.

Marred by political instability since independence in 1974, Guinea-Bissau became a key transit hub for cocaine in the mid-2000s for Latin American criminal networks seeking to ship the narcotic to Europe. At the peak of trafficking in 2007, almost 70 tons are believed to have passed through West Africa.

Trafficking routes changed after the U.N. and international law enforcement stepped in to bolster the judiciary and the police.

Since then, the estimated amount of cocaine flowing through the region has dropped to 40 tons per year, with a street value of $2.1 billion, according to an forthcoming paper from the Organization for Economic Cooperation and Development obtained by Bloomberg.

A sharp increase in global cocaine production led by Colombia in recent years could help explain the comeback of the West African route, with traffickers looking to diversify destinations, Shaw said. Unusually large shipments of cocaine seized along the U.S.-Mexico border in 2017 and 2018 appear to indicate that the output surge is emboldening drug gangs to take more risks, according to a 2018 report by the U.S. Drug Enforcement Administration.