MPs and relatives of those killed in the Omagh bomb will lay a wreath at a memorial garden in the town today.
Members of the Omagh Support and Self Help Group will then meet with the Northern Ireland Affairs Committee to ask for a full cross-border public inquiry into the atrocity.
The government has previously said an inquiry into the 1998 bombing in which 26 people were killed will not take place until a report commissioned by the group is completed.
The former chairperson of the Northern Ireland Affairs Committee, Sir Patrick Cormack, has acknowledged that there are unanswered questions about the Omagh bomb and has expressed his hope that the new committee would address these outstanding issues.
Four men have been held responsible by a civil court for the Real IRA bombing. A man accused of murder was cleared by a court in 2007.
A 2001 report by former Police Ombudsman Dame Nuala O`Loan criticised poor judgment in the RUC in the years after the attack, while relatives of those killed have called for a cross-border public inquiry into alleged failings by police, north and south.