During an event in Sonora, Lopez Obrador signed the decree that orders the energy ministry “to take the actions necessary to carry out” the nationalization process.

It also declares 234,855 hectares (907 square miles) in Sonora as a mining zone known as Li-MX 1.

“(Let’s make) the nation be the owner of this strategic mineral,” Lopez Obrador said during the event.

Mexico holds important potential lithium deposits, a highly sought material for the production of electric vehicle batteries.

Studies suggest Mexico may have some 1.7 million tonnes of lithium. While close to a dozen foreign companies have active mining concessions that aim to develop potential lithium deposits, Lopez Obrador has said all of them will be “reviewed,” which has cast a cloud over the sector’s future prospects.

“What we are doing now … is to nationalize lithium so that it cannot be exploited by foreigners from Russia, China or the United States,” Lopez Obrador said at the event.

Last week, the chief executive of the state-run company for lithium production, Pablo Taddei, told Reuters that Mexico was open to partnerships but that the federal government would have a majority stake in any future joint venture.

The decree published Saturday by the economy ministry said that “the rights and obligations of the holders of mining concessions in force that are within the lithium mining reserve zone remain safe.”

It adds that “no mining activity related to lithium” can be carried out within the reserve but gave few additional details.