The assembly government is investing to improve responses

The cross-party group told BBC Wales patients' lives were being put at risk.

Lib Dem Kirsty Williams, Conservative Glyn Davies and Plaid Cymru's Elin Jones want measures to improve the speed with which calls are answered.

The Welsh Ambulance Service NHS Trust said the response time target was challenging, but the situation had improved over the past 12 months.

The AMs told the BBC Wales current affairs programme Maniffesto on S4C on Sunday of their serious concerns for the safety of patients.

In one case, they said, a road traffic accident victim in Llandrindod Wells had to be taken to hospital by police after being left lying in the road for half an hour.

Llanidloes GP Dr Stephen Lesley told the programme that the region was "skating on thin ice" because of the slow responses.

Maniffesto said many of the trust's key targets were being missed.

Demands made

The trust aims to answer 65% of life-threatening calls within eight minutes - but, across Wales, only 57.5% actually are.

On Friday, the BBC news website reported how Llanidloes town council had demanded an improvement in the service.

Only in north Wales does the trust meet its response time goal.

Llanidloes mayor Robert Parker-Munn said: "Targets are not being met and we feel that this is putting lives in danger."

A Welsh Assembly Government spokesman said it was investing in the service.

"Since 2002-03, an additional �3.5m per year has been invested to specifically improve ambulance response times," he said.

"This year's target specifically require there to be improved performance in all geographic areas which are currently below our target to respond to calls that are immediately life-threatening."