US authorities have issued letters to an array of shipping companies in what industry sources see as an effort to put pressure on the tanker sector over the price cap on Russian oil.

Tanker market sources said the letters have been received by more than 30 shipowners and managers in the tanker space.

The US Treasury department’s Office of Foreign Assets Control, known as Ofac, sent the letters mostly to Greek companies trading in the crude and fuel oil trades impacted by the price cap.