Oil refining company Murco says it is investigating whether unleaded petrol from its plant in Milford Haven was contaminated by water.
It comes after a number of cars broke down after filling up at a Morrisons petrol station in Carmarthen.
We have been made aware that a number of deliveries of unleaded fuel from our Milford Haven Refinery may have been contaminated by water.
We are currently carrying out an investigation to determine whether such contamination has occurred at our site and its cause.
Until such time we complete our investigation we will maintain additional controls to ensure that any fuel leaving the site is free of contamination.
Supermarket chain Morrisons has issued an update after a number of cars broke down after filling up at its petrol station in Carmarthen.
It says a batch of unleaded petrol from the Milford Haven Refinery "may have been contaminated with water."
Deliveries to stores in Carmarthen and also Llanelli appear to have been from the affected batch.
Morrisons sources its unleaded petrol from the Milford Haven Refinery, which has confirmed to us that a batch of fuel may have been contaminated with water.
Deliveries to two Morrisons stores – Carmarthen and Llanelli – appear to have been from the affected batch. As soon as we became aware of the problem we immediately took the unleaded off sale at these sites.
We apologise to those motorists affected and are doing everything we can to support them. Customers affected will be reimbursed for their fuel, vehicle recovery and any repairs which are needed.
At least 17 drivers have seen their cars break down after filling up at a supermarket petrol station in Carmarthen.
Morrisons was forced to close the unleaded pumps at its station at Parc Pensarn retail park, and to apologise to customers.
Driver Marc Skone bought £40 of petrol, but only got 100 metres from the forecourt before his car broke down.
He said: "It has cost £150 plus VAT to drain the tank - something I can't afford with Christmas coming."
A recovery company in Carmarthen has picked up 17 cars this morning which had used the supermarket's pumps.
A spokeswoman for Morrisons said: "We have registered a water reading in two of our unleaded petrol tanks at Carmarthen petrol station."
"We apologise to these motorists for any inconvenience that this has caused, and are passing their details to the AA who will carry out any necessary repairs."
An inquest has been opened and adjourned into the death of three-year-old Angel Jade Keogh following a house fire in Carmarthen on the weekend.
"Our beautiful princess will be in our hearts and memories forever" said her family.
Her mother Alice Smith, 24, has now been released from hospital.
A mother has suffered a double tragedy - her little girl was killed in a house fire exactly a year to the day after her baby son died from cot death. Little Angel Jade Smith, three, died after a horrific blaze tore through her family home in Carmarthen.
The tragedy happened a year to the day that her baby brother Jake was found dead from suspected cot death at six months. Mum Alice Smith, 24, is in a serious condition in hospital after being rescued by firemen from the burning house on Sunday.
Family friend Lisa Naether said, "We were in total shock when we heard, especially as it was the anniversary of her baby brother's death." Neighbours called 999 after spotting black smoke billowing from the family home.
Firefighters arrived at the terraced house were they found Angel and mum Alice trapped inside although her father had escaped by jumping from a window.
Friends helped raise £300 for a headstone following Jake's death in June last year.
Dyfed Powys Police say a three-year-old girl has died after a house fire in Carmarthen yesterday evening.
Her mother - a woman in her twenties - remains in hospital in a critical condition.
The girl's father is also in hospital.
The cause of the fire has not yet been established.
A woman and a child are in a serious condition after a house fire in Carmarthen. Police officers are currently investigating what caused the blaze at Bryn y Gorwel yesterday evening. Fire officers were joined by police and paramedics at the scene at around 6.15pm.
A woman in her twenties was taken to Morriston hospital, whilst the child was sent to Glangwili. A man also needed hospital treatment. Dyfed-Powys police say next of kin and family are being supported by officers.
Bowel unit services at Bronglais Hospital in Aberystwyth are being 'downgraded by stealth' - a former surgeon there has claimed.
David Jackson says services are being centralised to Withybush Hospital in Haverfordwest.
For one woman that's meant spending thousands of pounds in travel and accommodation to visit her husband.
Linda Davies had assumed Meu would be treated 45 minutes away in Aberystwyth.
Instead they have to travel up to three hours to Haverfordwest. The local health board rejects the 'downgrading' claims. Kevin Ashford reports.
Concerns have been raised over claims that a bowel surgery unit at Bronglais Hospital in Aberystwyth is being downgraded by stealth and moved to Carmarthenshire with a massive impact on patients. Hywel Dda Local Health Board has rejected the claims.
Linda Davies' husband, Meu, was diagnosed with bowel cancer. His treatment has involved numerous hospital visits and overnight stays.
Linda had assumed that would mean travelling the 45 minutes from their mid-Wales home at Llanbrynmair to Aberystwyth for appointments at Bronglais Hospital.
Instead they've had to make half a dozen trips to Haverfordwest in Pembrokeshire for treatment at Withybush Hospital - a journey which can take up to three hours in the car.
There are claims that a bowel surgery unit at Bronglais Hospital in Aberystwyth is being downgraded by stealth and moved to Carmarthen.
It is thought the move could mean patients having to travel up to three hours for treatment.
Hywel Dda Local Health Board has rejected the claims.
Dr Sue Fish, Medical Director at Hywel Dda Local Health Board, said: "We openly announced some time ago that we needed to undertake a review of surgical services across Hywel Dda - including colo-rectal cancer surgery.
"That review is ongoing and we expect it to be completed within the next few months.
"Whilst this review is ongoing, our responsibility is to ensure that patients receive the highest standard of care possible."