A team of engineers from Mercedes-Benz in Germany will inspect the £16m fleet of 119 Sprinter vehicles that entered service last year.

They were hailed as the best ambulances in Britain until three fires in the last two weeks raised the alarm.

One of the fires happened in Bangor and another on the A55 with a third incident in South Wales.

Mercedes have reassured the Welsh Ambulance Service that the vehicles, which cost £133,000 each, could remain operational.

The Welsh Ambulance Service said they were treating the matter "extremely seriuosly".

A spokesman for Mercedes Benz said: "Mercedes-Benz is aware of the recent engine fires that have affected three ambulances operated by Welsh Ambulance. We have initiated an urgent investigation into these incidents to establish the cause. While that investigation is under way, we are naturally unable to comment any further."

A Welsh Ambulance Service spokesperson said: "I can confirm we have had three events of engine fires in our vehicles. We use standard Mercedes engines in our vehicles which have not been modified in any way.

"We are treating the events extremely seriously and have initiated an urgent investigation with Mercedes Benz.

"A preliminary investigation was carried out by the Mercedes-Benz UK Technical team and in addition, an investigations team from Germany have worked with the Trust to carry out more detailed investigations to establish the cause and necessary rectifying action.

"We are reassured that this matter has been escalated to the very highest level within the Mercedes-Benz organisation and it is being treated with the utmost priority.

"The welfare of our staff and patients is of utmost importance and we immediately issued a Health and Safety Alert Wales-wide to safeguard patients, staff and the public.

"In summary, the Trust is doing everything that could reasonably be expected of it to deal with the problem," he said.