* Tanker seizure victory for Tripoli government
* Eastern federalist want more oil share
* Libya army struggling to impose security (Adds details throughout)
By Hani Amera
TRIPOLI, March 23 (Reuters) - A commercial oil tanker that was seized and returned by U.S. forces after it loaded crude at a Libya port held by anti-government rebels has docked back in the capital Tripoli, a Reuters witness said on Sunday.
U.S. special forces seized the tanker a week ago off Cyprus, days after it left from Es Sider port, which is controlled by rebels who demand more autonomy and oil wealth in defiance of the central government.
A Reuters witness on the coast near Tripoli saw the Morning Glory offshore. The tanker was due to arrive later at Libya's Zawiya port, where its cargo of crude is to be fed into the Zawiya refinery.
It was a rare victory for Tripoli, which is struggling to end a port blockade, one of many challenges facing the weak central government which has failed to secure the North African country three years after the fall of Muammar Gaddafi.
Former anti-Gaddafi rebels and militias refuse to surrender their weapons and often use force or control of oil facilities to make demands on a state whose army is still in training with Western governments.
The crew of the Morning Glory, which was North Korean-flagged until Pyongyang disavowed the vessel, say armed Libyan rebels boarded the ship, forced them to load crude and to evade the Libyan navy sent to stop them. (Writing by Patrick Markey; Editing by Sonya Hepinstall)