Offshore helicopter safety has "significantly" improved following a spate of crashes but there is still more to do, according to aviation chiefs.

Regulator, The Civil Aviation Authority (CAA), said measures including a no-fly rule in the most extreme sea conditions had cut the risk of further North Sea deaths.

Operators must now ensure every passenger is equipped with a new, improved emergency breathing system (EBS).

The UK aviation regulator launched a review of offshore helicopter operations after five accidents between 2009 and 2013.

In April 2009, all 16 oil workers and crew aboard a Super Puma died when it crashed 14 miles off the Aberdeenshire coast.

In August 2013, a Super Puma crashed near Sumburgh airport in Shetland in August 2013, killing four people.

An interim report published today outlined progress on its recommendations and the improvements that have been introduced since last year's review.

Those related to helicopter design are "longer-term projects" but the CAA and the Offshore Helicopter Safety Action Group (OHSAG) will maintain pressure on the responsible organisations to deliver safety improvements as soon as possible, the CAA said.

Director of safety and airspace Mark Swan said: "The safety of those who rely on offshore helicopter flights is our absolute priority.

"Some encouraging progress has been made over the last year to improve helicopter safety but there is still more that can and will be achieved."

The report singled out EBS and new safety training for workers travelling. It said: "Today, flights no longer take place over the most extreme sea conditions. We believe these changes together will contribute to lives being saved in the UK offshore industry in the years to come."

Louise Ellman, chair of the Commons Transport Committee which had recommended an independent inquiry, said it was a "regrettable" decision for the loved ones of those killed in offshore accidents and sent out the wrong message to those continuing to work in the industry.

Sir Robert Smith, MP for West Aberdeenshire and Kincardine, wants to see new safety regulations speeded up. He said: "The improvements that have been made to safety training and emergency breathing equipment are welcome. However, there is still more that needs to be done."