Tuesday, August 18, 1998 Published at 04:57 GMT 05:57 UK
Five still held by RUC
No one has claimed responsibility for the bombing
Five men are still being questioned by police investigating Saturday's car bomb attack in Omagh.
All are being interviewed by the RUC in Belfast.
The bomb - the worst atrocity of the Troubles - claimed 28 lives and left more than 200 injured.
The 32-County Sovereignty Committee is one of three republican splinter organisations that remain implacably opposed to the Good Friday Agreement.
BBC Northern Ireland correspondent Mark Devenport said the denial would probably be viewed with scepticism by the people of Northern Ireland who could point to existing evidence of links.
Mr Mackey said, when asked if he condemned the bombing: "No amount of words from me will in any way alleviate the suffering of the bereaved and the injured.
"I have categorically stated that no justification, under any circumstances, can be made for what took place in Omagh."
UK Prime Minister Tony Blair has pledged that police on both sides of the border will get full support in finding the bombers.
"We are only going to defeat them if we take the security measures we can take, and make sure we are offering a different way forward for the future."
But on landing he had a phone call booked with Mr Trimble, and would remain "in constant touch" with Irish Taoiseach Bertie Ahern, said a Downing Street spokesman.
The spokesman added: "If it's necessary he will go back at any time.
"He has no doubt whatsoever that the peace process is strong enough to withstand this one event."
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