A third baby has died after an outbreak of a deadly infection in a Belfast hospital, it was confirmed on Friday.

The deaths at the city's Royal Maternity Hospital occurred in the last week to 10 days, but a possible link to the pseudomonas bacteria was only discovered recently.

The first two babies were born prematurely.

The latest death came as staff began an investigation to trace the killer bug at Northern Ireland's largest maternity unit, which will now undergo a deep clean.

The Belfast Health and Social Care Trust said the deaths, in the neonatal unit, may be linked to the outbreak of the infection, which can cause severe breathing and other problems.

Admissions to the unit have been restricted to all but the most seriously ill babies who cannot be treated elsewhere, but staff believe the infection has not spread to other areas of the Royal Victoria Hospital site.

Dr Richard Wright, associate medical director at the Belfast Trust said: "We are engaged in a fairly major investigation to identify the cause of the infection."

Northern Ireland's health minister Edwin Poots said expectant mothers are likely to be transferred to other hospitals in the Irish Republic and Britain.

"This is a serious incident," Poots said.

"I have asked the trust to work with the Public Health Agency to ensure all necessary steps are swiftly taken to identify the source of the infection so that we contain it and reduce the risk of spreading."

Pseudomonas aeruginosa is a bacteria that can survive in moist conditions and is particularly harmful to those who are already ill, including the elderly, or to premature babies who lack fully developed immune systems.