Ambulance emergency response times have fallen below their target in Wales for the first time in nine months.
The service has had 100 new ambulances bought recently
Figures for December 2007 show only 55.9% of the most important emergency calls received a response within eight minutes, compared to the 60% target.
BBC Wales also understands that the problems continued in January, with performance on these calls below 60%.
An internal report by the Welsh Ambulance Service said high seasonal pressures were to blame.
Unofficial overtime ban
It also blamed extended turnaround times for paramedics outside accident and emergency, alongside "factors related to availability of staff to fill rotas."
This is a reference to the unofficial overtime ban by staff in south east Wales over the Christmas period.
The corresponding target for the emergency Category A calls for the ambulance service in England is 75%.
The Welsh Ambulance Service had seen an improvement in its performance during 2007 after new management was introduced the previous year.
There was also an improvement in the service's resources with £16m invested in 100 new ambulances
Last March performance figures appeared to be going in the right direction and the service hit the 60% target of getting to enough category A calls within eight minutes.