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.

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Alongside the frigate’s contact with the Jal Laxmi, the U.S. and United Nations also exerted pressure behind the scenes to block the shipment, three of the diplomats said. The UN’s Panel of Experts and sanctions committee have warned all parties involved that they were violating an embargo, one of the diplomats said.

Read more: Bloomberg