Officers investigating the matter have yet to establish whether the drugs in circulation are too pure or possibly contaminated.

Heroin use is a growing problem in the south Wales Valleys

Drug user Richard Paul Smith, 33, from Tonypandy, south Wales, died on Monday.

Another man, thought to be in his 20s, died on Wednesday and has yet to be named.

South Wales Police Detective Inspector Paul Burke said he was concerned by the series of recent events.

"We would warn drug users that they could be at even more risk should they use this batch of heroin."

A national alert was issued last month after contaminated heroin, blamed for at least 31 fatalities across Britain and Ireland last year, was linked to a drug user who was taken ill.

Deaths in Glasgow, Aberdeen, Dublin, England and Wales were all being linked to the rogue batch.

In March, South Wales Police warned that heroin use in the Valleys could reach epidemic proportions.

In the Rhondda Cynon Taff area, home to 250,000 people, it is estimated that 12 people every week overdose on the class A drug.

Anti-drug group Raid was set up by worried Rhondda residents in partnership with local police, in a bid to reduce the number of incidents.