Universal Fish Company (UFC), Ukraine's largest salmon importer and processor has returned to previously Russian-occupied Kupyansk to find its processing plant there destroyed by fighting.

It is the company's second loss of key facilities since Russian attacks on the country began in February.

"We all congratulate the liberation of our native Kupyansk, but we are in great amount [of] sadness," a company spokesperson wrote on Facebook.

"UFC has been hit by the fascists for a second time," it said, referencing video footage of its former factory, now an empty, burnt out shell.