FIFA has signed state-controlled diamond miner Alrosa as a fourth Russian sponsor, completing its slate of third-tier European backers for the World Cup.

FIFA describes Alrosa as a "giant in the world diamond mining industry." The value was not disclosed.

Alrosa joins Alfa-Bank, Rostelecom and Russian Railways as World Cup sponsors in a regional category created for the 2018 tournament. The 16 other regional slots — for North and Central America, South America, Africa and the Middle East, and Asia — are still empty ahead of the June 14 kickoff.

Russian state energy firm Gazprom is among seven top-tier sponsors.

FIFA has signed World Cup sponsors only from Russia, China and Qatar since being rocked by Swiss and American federal investigations of corruption in 2015.