Turkey sent between 3,500 and 3,800 paid Syrian fighters to Libya over the first three months of the year, the U.S. Defense Department’s inspector general concluded in a new report, its first to detail Turkish deployments that helped change the course of Libya's war.

The report comes as the conflict in oil-rich Libya has escalated into a regional proxy war fueled by foreign powers pouring weapons and mercenaries into the country. The U.S. military has grown increasingly concerned about Russia’s growing influence in Libya, where hundreds of Russian mercenaries backed a campaign to capture the capital, Tripoli, in the country's west.

The quarterly report on counterterrorism operations in Africa by the Pentagon's internal watchdog, published Thursday, says Turkey paid and offered citizenship to thousands of mercenaries fighting alongside Tripoli-based militias against troops of east Libya-based commander Khalifa Hifter.