The two men, aged in their 40s, were arrested in Dublin and are being held under Section 30 of the Offences Against the State Act at a Dublin Garda Station.
Detective Superintendent Sean Wright said: “I welcome this development and it demonstrates the excellent working relationship between PSNI and AGS. The arrests should send a clear message to those involved in terrorist activity that the border does not provide an escape route.
“Our two police services work collaboratively on a daily basis, sharing knowledge and information, to ensure that there is no hiding place for criminals or terrorists.
“My detectives continue to investigate this reckless attack on a public servant and we have considerable support from our AGS colleagues. If you have information about the incident or you suspect that someone you know is a member of a dissident republican group, then contact detectives on 101 or let us know through the confidential Crimestoppers number on 0800 555 111.”