Authorities are monitoring parts of the north Wales coast for an oil slick after hydrocarbons were released into the sea following a pipeline failure.

The pipeline, which connects two oil installations in the Irish Sea, had a failure about 20 miles from the north Wales coast. According to Eni UK, the company that operates the pipeline, the incident involved less than 500 barrels and was reported on Monday.

The company confirmed that hydrocarbons had been released from its pipeline running between Conwy and Douglas oil installations, sparking fears of an oil slick.

It said: “Eni UK Ltd can confirm that a release of hydrocarbons from its pipeline between the Conwy and Douglas installations, approximately 33km from the north Wales coast, was reported on Monday 14 February.”

It said the details of the incident were still being confirmed but the “Conwy to Douglas line was shut immediately and remains off”. It added: “All relevant authorities were promptly informed. There was no impact at any personnel on the installations. A further statement will be made as soon as more information becomes available.”

A spokesperson for the Maritime and Coastguard Agency said it was monitoring Eni UK’s response and assisting local authorities.

News of the spill came on the 26th anniversary of what has been called Wales’ worst ecological disaster, when 72,000 tonnes of crude spilled from the Sea Empress oil tanker off the Pembrokeshire coast. Large numbers of seaweeds and invertebrates were killed on the beaches where it drifted ashore, and it took over a year to clean the slick.

Doug Parr, the chief scientist for Greenpeace UK, said: “This week marks the anniversary of the Sea Empress oil spill. A quarter of a century on, we still find that oil is a dirty business at every stage, whether that’s through planet-warming emissions or leakages like this that harm marine life. The ongoing environmental damage oil causes should be a major incentive to drive forward the cleaner, cheaper energy technologies that now exist.”

Dr Richard Benwell, the CEO of Wildlife and Countryside Link, said: “It’s 26 years to the day since the Sea Empress disaster wrought ecological havoc on the Welsh coast … Fossil fuel spills are again threatening the wildlife in our waters, which are already in a precarious state. The sooner we break our dependence on these dirty fuels the better.”