A deadly infection which killed four babies in Northern Ireland has been discovered in the taps at a hospital.

The pseudomonas bacteria was uncovered at the neo-natal unit at Altnagelvin, Londonderry, where an infant died before Christmas, the Public Health Agency (PHA) said.

Steps have been taken to ensure newborns do not come into contact with the infected supply and only sterile water is used for their direct care. No babies are infected but two have it on their skin.

A PHA spokeswoman said: "Water sample results for the Western Trust show that pseudomonas has been detected in a small number of water outlets in the neonatal unit at Altnagelvin. As in all neonatal units, including Altnagelvin, steps had already been taken to ensure that babies are not coming into contact with the water supply."

Separate outbreaks claimed the lives of one newborn at Altnagelvin in December and three at the Royal Jubilee Maternity Hospital in Belfast this month.

Health trusts may not have acted quickly enough to prevent hospital outbreaks of the deadly infection, the Stormont health minister has said.

Announcing an independent investigation into the pseudomonas bacteria emergencies in three neonatal units, Edwin Poots told the Assembly that the actions of trust officials needed to be rigorously examined.

Traces of the infection were also detected in the neonatal unit at the Ulster Hospital on the outskirts of Belfast at the weekend, though no infants contracted it.

The parents of one of the four babies who died from pseudomonas had called for a public inquiry.

Gavin Burke and Caoimhe Campbell's 10-day-old son, Caolan, died in the neonatal unit in Derry last month. Ms Campbell said last week: "He would still be here only for that infection. We want a public inquiry into this because it'll get at the truth."