Europe will attempt to launch a Russian Soyuz rocket for the fourth time Monday after weather conditions and technical faults halted previous take-offs, launch service Arianespace said.

The launch from French Guiana was initially scheduled for Friday and was to be Europe's first of the year from the South American space centre.

"Operations to replace the central inertial unit of the Soyuz VS14 are currently underway," Arianespace said in a statement Sunday. "The launch is now scheduled for Monday 25 April 2016 from Kourou at 18.02 local time (2102 GMT)."

A countdown on Sunday was halted after scientists observed an "anomaly", the company said in an earlier statement, while adverse weather conditions had thwarted other attempts.

The rocket is set to launch Microscope, a French-built orbiter seeking to poke a hole in Einstein's theory of general relativity, and satellite Sentinel-1B.

The satellite is the twin of Sentinel-1A, launched two years ago.

The pair are equipped with sophisticated, cloud-penetrating radar to monitor Earth's surface by day and night, regardless of the weather conditions.

Their mission is to track climate and environmental change and assist in disaster relief operations.

Sentinel-1A and 1B are part of the 3.8-billion-euro ($4.3-billion) Copernicus project, which will ultimately sport six orbiters in all. It is a joint undertaking of the European Space Agency and the European Commission.

The Soyuz will also boost into orbit three so-called "CubeSats", tiny orbiters built by European science students.