A section of the railway line has been closed since Friday
Shots have been fired at police officers investigating a security alert in County Down.
Security forces have been examining a suspicious object close to a railway line outside Newry since Friday.
District Commander Chief Superintendent Alisdair Robinson said the attack was "a cowardly attempt to kill police officers".
Sinn Fein MP for Newry and Armagh Conor Murphy said those who carried out the attack were "stuck in the past".
"These micro groups have disrupted the Dublin-Belfast railway line since Friday, inconveniencing business and leisure travellers alike," said Mr Murphy, who is also transport minister.
"They must know that they have no support in the community for this type of activity.
"Additionally, their unsuccessful attempts on the lives of PSNI officers who were attempting to return the railway line to operation is neither supported by myself or the vast majority of people in the locality."
No-one was hurt during the attack which happened at about 2115 GMT on Saturday.
Police have appealed for information.
Ch Supt Robinson thanked the local community for their patience as they investigated the alert.
"The people who carry out these senseless acts show a total disregard for their fellow man and are not part of the society within which the majority of people of Northern Ireland wish to live," he said.
"Officers will continue to look after the policing needs of all our people and will put in place whatever measures are necessary to take a robust stance against those who seem determined to disrupt and attack local communities."