The Garda National Drugs Unit is conducting an urgent investigation on foot of a significant spike in the number of suspected drug-related deaths in the Dublin area since the start of this month.

The move comes amid fears that vulnerable heroin users may be at risk from a potentially lethal batch of the drug.

While officials say it is still too early to establish a direct link between the deaths of at least four people in the space of 24 hours in the north and south inner city, there are concerns that the actual number of deaths could be as high as 10 since the start of the month.

This has prompted local drugs task forces and treatment providers to begin advising drug projects, services and their clients of the risks by putting up safety warning signs in clinics.

According to internal correspondence seen by the Sunday Tribune, at least three people died over a 24-hour period in the south inner city/canal area from suspected heroin use at the beginning of this month.

There was a similar death in the north inner city at that time, while there have been reports of other recent drug deaths in the Tallaght area.

A spokesman for the Department of Justice confirmed that it had received reports of a number of suspected drug-related deaths over a short period of time in Dublin earlier this month.

"We understand that a safety warning message was issued by drug task forces and treatment providers to drugs projects, services, clients and users," he said. "We have been advised that the health authorities have been liaising on these matters with the Dublin city coroner, who has legal responsibility for the independent investigation of all sudden and unexplained deaths."

"In conjunction with this we understand that the Garda National Drugs Unit is also currently examining possible links between the reported deaths, including the possibility of the use of a bad batch of heroin being implicated in such details. This investigation is ongoing."

A spokeswoman for the minister of state with responsibility for drugs, John Curran, said his office is also aware of the problem.

"The minister understands that drugs task forces and service providers are advising problem drug users to be aware that there may be particular dangers at this point in time in the use of drugs," he said.

"They are being advised that if they are going to use drugs the message is to take smaller doses. Information in regard to dealing with problems should they arise is also being given."