A man and a woman have been arrested in connection with the Omagh bombing.
The pair were detained for questioning in the Jonesborough area of County Armagh on Tuesday.
Twenty-nine people died in August 1998 in the Real IRA bombing of the County Tyrone town, which was the worst single atrocity in 30 years of violence in Northern Ireland.
Since then hundreds of people have been arrested in connection with the incident but no one has actually been charged with placing the bomb
The two people held will be questioned in connection with a number of terrorist related offences.
It is understood 200 police officers and Army personnel were involved in the arrest operation.
In January 2002, father-of-four Colm Murphy became the only person to be convicted of plotting the Omagh bombing.
The Special Criminal Court in Dublin sentenced the Dundalk-based builder and publican to 14 years in jail.