The cross-border railway line and the Newry bypass have reopened after police recovered a device near the track during a security operation.
The device partially exploded on the railway line
The device, which had already exploded, caused minor damage close to the railway line. Trains were disrupted over the weekend during the search.
One youth has been arrested after police were attacked with up to 30 petrol bombs on Sunday on the bypass.
The dissident republican Real IRA said it had left two devices on the line.
Last Wednesday, police found a separate device which had also exploded.
The Real IRA said on Friday it had also carried out firebomb attacks in Newry which destroyed a number of shops.