Environmental groups are suing a US government agency over concerns that oil exploration in Alaska could kill off endangered Beluga whales.

They want to force the National Oceanic and Atmospheric Administration (NOAA) to void a permit allowing exploration in waters used by the whales in the Cook Inlet.

It comes after a new population report showed that the whales are fewer in number and declining faster than previously thought.

The new estimate says just 279 beluga whales are left in the Cook Inlet, down from 1,300 in 1979.

The decline amounts to around 2.3 per cent over the past decade, “daunting” numbers which need to trigger immediate action to stop exploration planned by Hilcorp Energy Company, according to the Center for Biological Diversity.

Tragic photos show beached whales Show all 15 1 /15 Tragic photos show beached whales Tragic photos show beached whales A dead sperm whale lies on Hunstanton beach in Norfolk on 5 February 2016 AFP/Getty Tragic photos show beached whales Volunteers pour buckets of water over the 80 remaining live pilot whales found stranded on remote Ocean Beach on New Zealand's southern-most Stewart island, 8 January 2003 AFP/Getty Tragic photos show beached whales Contractors clear away the body of one of the dead 48ft sperm whales that were washed-up on a beach near Gibraltar Point in Skegness, Lincolnshire in 2016 PA Tragic photos show beached whales People pass by a beached whale at the Pointe de la Torche, near Brest in France on 29 November 2011 AFP/Getty Tragic photos show beached whales A woman touches the tail of a large whale carcass on Wattamola Beach at the Royal National Park in Sydney on 25 September 2018 AFP/Getty Tragic photos show beached whales Beached humpback whale in California, 2015 AFP/Getty Tragic photos show beached whales Dead long fin pilot whales at Hamelin Bay on Australia's west coast on 23 March 2009 AFP/Getty Tragic photos show beached whales A 36ft sperm whale lies dead on the beach at Sutton Bridge, in The Wash, off the Lincolnshire coast, where it became stranded in 2004 PA Tragic photos show beached whales A female fin whale opens its mouth as it lies stranded and alive on the beach at Carlyon Bay, Cornwall on 13 August 2012 Getty Tragic photos show beached whales The lower jaw of a dead sperm whale that stranded itself on a beach in Hunstanton, Norfolk on 5 February 2016 Getty Tragic photos show beached whales One of the five sperm whales that were found washed ashore on beaches near Skegness, Lincolnshire over the weekend on 25 January 2016 Getty Tragic photos show beached whales Employees at work to skin the remains of a beached 60ft whale on 25 January 2013 AFP/Getty Tragic photos show beached whales Two long-finned pilot whales are stranded on a beach in the northern French city of Calais on 2 November 2015 AFP/Getty Tragic photos show beached whales A sperm whale lies dead after becoming stranded on a beach in Hunstanton, Norfolk on 5 February 2016 Getty Tragic photos show beached whales Crowds gather as a sperm whale lies dead after becoming stranded on a beach in Hunstanton, Norfolk on 5 February 2016 Getty

The group’s attorney, Julie Teel Simmonds, said there’s a duty to reconsider and ‘analyse if there's new information that's significant and indicates that the activities that they authorised would cause harm’. The community non-profit organisation Cook Inletkeeper is also suing the NOAA.

The situation has emerged as a result of August’s loosening of environmental restrictions by the Trump administration.

The revised rules clear the way for new mining, oil and gas drilling, according to environmental campaigners, as well as development in areas where protected species live.

The Cook Inlet stretches almost 200 miles from Anchorage to the Gulf of Alaska, and supplies energy for the south-central area of the state.

Beluga whales swim off the Anchorage waters and eat salmon and other fish, but their existence is made precarious by their proximity to Alaska's industrial activities in Cook Inlet.

While the Cook Inlet region is Alaska’s oldest oil-producing basin, it’s not just oil exploration that threatens the Beluga whale; heavy ship traffic, industrial noise, pollution and climate change are all concerns.