The dissident republican Real IRA has claimed responsibility for the firebomb attacks on stores in Newry this week.
Fires engulfed a number of businesses in the city
Firebombs destroyed JJB Sports and CarpetRight stores in the town whilst a TK Maxx store and MFI outlet were among those badly damaged on Wednesday.
Meanwhile, the cross-border railway line between Newry and Dundalk has been closed while police carry out a search.
It follows the Real IRA's warning in its statement that there may be unexploded devices on the line.
The firebomb attacks earlier this week are estimated to have caused damage worth hundreds of thousands of pounds.
Newry's SDLP mayor Michael Carr said: "The Real IRA should examine their motives.
"Their cause is not a blow for Ireland, but a blow against their own communities."
Mr Carr added that the businesses which had been targeted would be given every support, including an effort to have them temporarily re-located.