June 28 (Reuters) - U.S. energy company Equitrans Midstream Corp's long-delayed $6.6 billion Mountain Valley natural gas pipeline received authorization on Wednesday from the country's energy regulator to restart construction of the project.

"Mountain Valley has all necessary authorizations for the Mountain Valley Pipeline Project, ... therefore authorized to proceed with all remaining construction associated with the project," the U.S. Federal Energy Regulatory Commission (FERC) said.

FERC had suspended work on Mountain Valley, a pipeline from West Virginia to Virginia, due to litigation over the project's Biological Opinion from the U.S. Fish and Wildlife Service, which allows construction in areas inhabited by endangered and threatened species.

Mountain Valley is one of several U.S. oil and gas pipelines delayed by regulatory and legal fights with environmental and local groups that found problems with federal permits issued by the Trump administration.

Mountain Valley is owned by units of Equitrans, NextEra Energy Inc, Consolidated Edison Inc, AltaGas Ltd and RGC Resources Inc.

(Reporting by Akanksha Khushi in Bengaluru; Editing by Leslie Adler)