A rescue operation involving tugboats, helicopters and more than 50 personnel saw 13 crew members rescued from one tanker, before being suspended due to bad weather.

The 14 remaining crew members aboard the second tanker are said to have “everything necessary for immediate life support” on board with them, but look set to be stranded until conditions improve.

President Vladimir Putin has ordered a working group to be set up to deal with the incident, headed by Deputy Prime Minister Vitaly Savelyev – and authorities are investigating for criminal negligence.

Michelle Bockmann, an analyst at shipping industry journal Lloyd’s List, told the BBC the two vessels are owned by the company Volgatanker and were relatively small.

They had been carrying around 4,300 dead weight tonnes of oil each, according to Russian officials quoted by Tass news agency.

A tanker used for trading Russian crude oil internationally generally has a much larger carrying capacity of around 120,000 dead weight tonnes, Bockmann said, meaning it is likely these tankers were used for transporting oil through Russia’s rivers or in coastal waters.

The Kerch Strait is a key route for exports of Russian grain and it is also used for exports of crude oil, fuel oil and liquefied natural gas.

In 2007, another oil tanker – Volgoneft-139 – split in half during a storm while anchored off the Kerch Strait, spilling more than 1,000 tonnes of oil.

Russian oil imports have been heavily sanctioned by allies of Ukraine since the Kremlin ordered the full-scale invasion of the country in February 2022.

In recent years, Russia has been accused of using a so-called ghost fleet of tankers, which are often poorly maintained and lack proper insurance, to move oil and circumvent sanctions – though Bockmann said it did not appear the tankers involved in Sunday’s incident were part of that fleet.

Additional reporting by Joshua Cheetham