Two Russian oil tankers with 29 crew members on board have been heavily damaged in the Black Sea, triggering an oil spill, authorities in Russia have said.

Footage released by Russia's Southern Transport Prosecutor's Office showed one of the tankers broken in half and sinking amid a heavy storm, with streaks of oil visible in the water.

At least one crew member was reportedly killed. The second ship was said to have drifted after sustaining damage and conflicting reports suggested it may have later run aground.

The incident took place in the Kerch Strait, which separates Russia from Crimea - the Ukrainian peninsula illegally annexed by Moscow in 2014.

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.

A rescue and clean-up operation is said to be under way involving tugboats, helicopters and more than 50 personnel.

"Today, as a result of a storm in the Black Sea, two tankers, Volgoneft-212 and Volgoneft-239, sank," Russia's federal sea and inland water transport agency, Rosmorrechflot, wrote in a statement.

"There were crews of 15 and 14 people on board the ships. The accident resulted in a spill of oil products," it continued.

Michelle Bockmann, an analyst at shipping industry journal Lloyd's List, said the two vessels are owned by the company Volgatanker and had a carrying capacity of around 3,500 dead weight tonnes of oil each.

The tankers are relatively small, Bockmann told the BBC. She said a tanker used for trading Russian crude oil internationally generally has a much larger carrying capacity of around 120,000 dead weight tonnes.

She said the stricken tankers were likely used for transporting oil through Russia's rivers or in coastal waters.

The full extent of the oil spill and the exact fate of both ships remains unclear.

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 Ukraine 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