Metro told riders early Monday to expect delays on rail service to Greenbelt, in connection with the presence of an unauthorized person on the tracks.

In a service alert posted around 1 a.m. Metro told Green Line passengers that the intruder on the tracks was reported near the Archives station.

It was not clear when the unauthorized person was detected, or what the person was doing on the tracks.

Normally the last train to Greenbelt is scheduled to arrive about 12:40 a.m.