Four crew members from a Russian fishing boat were found dead after a vessel caught fire off the southeastern coast near Ulsan on Friday morning, while the other 21 were rescued, the Russian Embassy in Seoul and South Korea’s Coast Guard said Friday.

All 25 crew members were Russian nationals, and two crew members who were rescued have reportedly sustained minor burns.

Russia’s Ambassador to South Korea, Andrey Kulik, was quoted saying that he would like to “express his deepest gratitude to Korea’s Coast Guard for rescuing 21 crew members and for its effort in searching for those missing,” according to the Ulsan Coast Guard.

The 769-ton boat carrying 100 tons of fish and seafood in the waters off Ulsan caught fire at around 12:43 a.m., coastal authorities said. Rescue ships were immediately dispatched to the scene after a report was filed to the coast guard, but four people were missing. The fire was extinguished 13 hours after it broke out.

The Ulsan Coast Guard plans to look into the exact cause of the fire.