The departure of two Russian cosmonauts and one US astronaut from the International Space Station was delayed Friday because of problems with the docking port, dpa reported.
Engineers were examining the port's hooks and latches, delaying the space travellers' return to Earth by two orbits, the US space agency said.
The undocking was originally scheduled for 0135 GMT Friday but has been delayed until 0440 GMT, the National Aeronautics and Space Administration (NASA) said.
Mission Control in Moscow requested the crew remaining in the space station to open the hatch on the station's docking module to try to rectify the problem as American Tracy Caldwell Dyson and Russians Alexander Skvortsov and Mikhail Kornienko remained inside the Soyuz craft that is to return them to Earth.
The trio has been stationed on the orbiting outpost 350 kilometres above the Earth since April, tasked primarily with conducting scientific experiments.
The Soyuz capsule is now scheduled to return them to Earth at 0805 GMT, landing north of Arkalyk in Kazakhstan, NASA said.
The station's crew is schedule to be replenished with the takeoff October 7 of a Soyuz capsule from the Russian space centre at Baikonur, Kazakhstan, with cosmonauts Alexander Kaleri, Oleg Skripochka and astronaut Scott Kelly on board.