(Bloomberg) -- A French navy frigate hailed a tanker as it was on its way to load refined petroleum products from an eastern Libyan port, preventing it from reaching its destination and leaving it loitering offshore for almost a week, four Western diplomats told Bloomberg on Thursday.

The French Cassard class frigate “Jean-Bart” was on an EU mission named Irini that aims to enforce a weapons embargo on Libya and block illicit oil sales that could fund the warring parties, the people said, asking not to be named because the information hasn’t been made public.

The Jean-Bart approached the Jal Laxmi tanker on May 22 after Irini received information that it was headed to the port of Tobruk, as part of a sale of refined products to a company registered in the United Arab Emirates, the diplomats said. The tanker did not continue on its journey but remains in the area, they said.

France’s defense ministry didn’t immediately respond to requests for comment on the incident.

A military commander from eastern Libya, Khalifa Haftar is at war with the internationally recognized government in Tripoli. Haftar has been supported by the UAE, Russia and Egypt, while the Tripoli government is primarily supported on the ground by Turkey. Haftar controls most of the country’s oil fields, which tap into Africa’s largest reserves.

In an effort to pressure his opponents in the nation’s capital in January, Haftar allowed loyalists to shut down oil production. The Tripoli-based National Oil Corporation, which is in charge of output, said on Thursday that losses from the shutdown have cost the war-torn nation more than $4.9 billion in revenue.

The war took a turning point over the last month when Turkey’s military intervention forced Haftar’s self-styled Libyan National Army and hundreds of Russian mercenaries to withdraw from much of the territory they’d seized since starting their offensive in April last year. The U.S. said earlier this week that Russia has sent 14 fighter jets to support Haftar, in a sign of more direct Russian involvement in a conflict that has killed at least 2,000 people.

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