HOUSTON, May 24 (Reuters) - Oil major Shell on Tuesday said planned maintenance at its Mars platform in the Gulf of Mexico was completed on Sunday.

Shell, the leading operator in the U.S. Gulf of Mexico, last week said its Mars and Ursa platforms were in the midst of turnarounds, which started at the end of April.

The turnaround at Ursa is likely to be completed in early June, Shell said. (Reporting by Arathy Somasekhar in Houston; Editing by Tom Hogue)