The Pentagon revealed the boarding operation, which was run with helicopter support from the guided missile destroyer USS Roosevelt, took place in international waters southeast of Cyprus.

"No one was hurt tonight when US forces, at the request of both the Libyan and Cypriot governments, boarded and took control of the commercial tanker Morning Glory, a stateless vessel seized earlier this month by three armed Libyans," Pentagon Press Secretary Rear Admiral John Kirby said.

While he said it was a stateless vessel, previous and ongoing press reports indicate the vessel was North Korean-flagged and loaded up with more than 200,000 barrels of crude that belonged to Libya's national oil company.

The tanker and its "illicitly obtained" oil cargo will be sailed back to a government-controlled Libyan port by the US Navy.

Es-Sider is one of three eastern ports seized by protesting provincial forces led by former militia leader Ibrahim Jathran last year.

Analysts are increasingly concerned that Libya could plunge into civil war.