Officials in the Democratic Republic of Congo seized thousands of tons of copper and cobalt, prompting the justice minister to order an investigation into allegations of widespread illegal mining.

The confiscations came after a commission of officials from the police, military and mines ministry visited copper-rich southeastern Lualaba and Haut-Katanga provinces, the justice ministry said in a statement Monday posted on X.

“These operations have resulted in the seizure of more than 500 trucks and other vehicles and machinery, as well as several thousand tons of copper and cobalt,” the ministry said.

Justice Minister Guillaume Ngefa Atondoko Andali ordered an investigation into the commission’s findings, which may have uncovered “mining fraud, illegal exploitation of mineral resources and mineral smuggling,” the ministry said.

Congo is the world’s largest source of battery metal cobalt and the second-biggest copper producer. It has struggled to prevent incursions by illegal miners — often protected by Congolese security forces — onto sprawling concessions held by international companies including Glencore and CMOC Group.

The justice ministry said the seizures took place at several locations in the two provinces, notably at Menda in Lualaba.

Eurasian Resources Group has licenses in that area, and the company has been increasingly vocal in recent months about illicit mining on its concessions including the firm’s flagship Metalkol operation. ERG didn’t immediately respond to messages requesting comment outside normal business hours.

Last week, the United Nations’ Radio Okapi reported that more than 60 foreign nationals had been detained at Menda amid allegations of illegal mining and immigration violations. Congolese civilians and military personnel were also arrested in the operation, Radio Okapi said, citing unnamed local sources.

The promised investigation into illegal mining in Congo’s copper belt follows the suspension of a key mining regulator, and the detention of hundreds of Chinese miners, in recent weeks.

Chinese companies such as CMOC and Zijin Mining Group account for most copper and cobalt output in the central African country. Some smaller operators from China run processing plants but don’t have their own mines, meaning they source ore on the open market.