Republicans back inquiry on Omagh bomb
The assistance would expose alleged Police Service of Northern Ireland incompetence and throw light on claims that police officers knew of the attack in advance, Mr McGuinness claimed. He said: "Republicans would be only too glad to co-operate with any independent, international investigation into the bomb explosion, because we think the PSNI themselves have questions to answer.
He added: "There's a very strong belief within Irish republicanism that the PSNI not only failed to investigate the Omagh bomb properly, but that the RUC actually knew about the bomb before it took place."
The families of some of the 29 people murdered in the dissident Real IRA massacre viewed Mr McGuinness's declaration as a significant advancement on Sinn Fein's previous position on the bombing.
Michael Gallagher, who lost his son Aiden in the August 1998 attack, said: "This is progress, and something we welcome.
"It was unexpected that he said that, and we would be interested to hear now how Sinn Fein and the deputy first minister are going to move this forward."
The families' demands for an independent inquiry into Omagh, a case plagued by controversy over what intelligence senior police possessed and passed on to officers on the ground, comes amid their protracted civil action against five men suspected of involvement in the bombing.
The multi-million pound case which is due to be heard at the High Court in Belfast has been hit by further delays.