ISTANBUL (AP) — Three oil tankers were attacked by drones Thursday off Turkey’s Black Sea coast, a shipping agency said.

The ships all appear on Western sanctions lists as part of a “shadow fleet” exporting Russian oil and petroleum products and evading Western sanctions on Moscow because of its war in Ukraine. One was previously targeted in March.

Tribeca Shipping said the Palau-flagged ship James II was sailing 80 kilometers (50 miles) north of Turkeli district in Sinop when it was attacked. It was not carrying any cargo.

The Altura and Velora, both flagged to Sierra Leone, were targeted while carrying out ship-to-ship operations in a nearby area, according to a statement from the agency cited by Turkish media.

The crews of all three ships were unharmed. Turkish coast guard vessels were dispatched to assist.

There was no immediate claim of responsibility for the attacks, and Turkish officials were unavailable for comment.

The Altura was previously struck by a naval drone on March 26 as it approached the Black Sea entrance to the Bosporus, damaging its bridge and engine room.

The Altura and Velora belong to Turkey-based Pergamon Shipping, according to the OpenSanctions website, which tracks people or organizations involved in sanctions evasion. The James II is owned by the Marshall Islands-registered James Navigation.

In November, the Turkish government condemned Ukrainian drone attacks on two oil tankers in the Black Sea as posing “serious risks to navigation, life, property and environmental safety in the region.”

Ukraine has carried out successful naval strikes against Russian shipping during the war, particularly using explosives-packed marine drones. However, Ukrainian missions were previously largely limited to the waters of the northern Black Sea.