The Government has insisted it remains 100% committed to the long-awaited national children's hospital as it ordered experts to explain why planners rejected the Mater site.

The 650 million euro design must be scaled back or relocated after Health Minister Dr James Reilly revealed the plan failed despite close contact between architects and planning authorities.

An Bord Pleanala refused permission for the controversial north Dublin site, warning the 16-storey glass building was not sustainable and would overwhelm the Georgian district.

Dr Reilly assured parents of sick children that the Government will build the hospital despite the setback, saying: "We shall now sit down, examine very closely the Bord decision and make a determination very rapidly with great urgency and immediacy."

Former Health Service Executive chairman Dr Frank Dolphin will spearhead the review and make recommendations on how plans for the 400-bed Children's Hospital of Ireland can progress.

An Bord Pleanala inspectors - who did not consider clinical aspects - warned that the 74m-high building over 100,000 square feet was too large and out of place in the city skyline. Dr Reilly said he would discuss the decision with O'Connell Mahon architects/NBBJ who designed the structure and consulted planners.

It has been estimated that 33 million euro has been spent to date. Funding of 200 million euro had been earmarked from the sale of a new National Lottery licence with the winning bidder tied to an upfront payment.

The National Children's Hospital development board, said to have been disappointed by the refusal, is scheduled to meet next Tuesday to plan the next step.

Alternative locations are also now back on the table including co-location at Tallaght Hospital, co-location at James Connolly in Blanchardstown, a new standalone paediatric centre at Newlands Cross and redeveloping St James' and Crumlin in Dublin.

Ray Martin, spokesman for the New Children's Hospital Alliance, which opposed the Mater site, said an alternative would ensure easier access for parents: "Some 65% of patients are from outside the Dublin area, from places as far away as Donegal and Belfast. Travelling into a busy city was just a very bad idea. Building it on the outskirts would have meant a hospital for all the country."