A service to mark the 25th anniversary of the Omagh bomb is to take place in the County Tyrone town later.
Twenty-nine people, including a woman pregnant with twins, died in the 1998 Real IRA car bomb attack.
It was the greatest single loss of life in the history of the Northern Ireland Troubles – no one has been convicted of carrying out the attack.
In February, the UK government announced an independent statutory inquiry into the Omagh bombing.
Bereaved families had been campaigning for an inquiry for more than a decade.