TRIPOLI/LONDON (Reuters) - What began late last year as a routine new assignment for Pakistani sea captain Mirza Noman Baig ended in a dramatic night-time rescue as U.S. special forces seized the ship his family said he was forced to operate by Libyan rebels.

U.S. Navy Seals took control of the Morning Glory oil tanker in international waters off Cyprus on Sunday night, along with a cargo of oil that U.S. officials said had been stolen from the Libyan people, whose fragile government Washington supports.

Libya says gunmen demanding regional autonomy and a share of oil wealth managed to load crude onto the ship, which then escaped its navy. The embarrassment to the government in Tripoli prompted parliament to sack the prime minister.

Industry sources say much about the tanker has been a mystery since it showed up in eastern Libya nearly two weeks ago; the identity of its owner and operator were unknown, as was its ultimate destination and the buyer of its cargo.

According to Captain Baig's $9,000-a-month contract, sent to Reuters by his family in Karachi, the operator was Dubai-based Saud Shipping, part of the ZAD Group of companies, which trades and moves oil around the Gulf.

The contract, signed in November, is on paper with a Saud Shipping letterhead and is stamped and counter-signed by the firm.

Baig's family say the captain received direct orders from Saud Al Anazi, the head of ZAD Group, to stop near a rebel-held eastern Libyan port. Here, according to Baig's family and Libyan officials, armed men boarded and loaded the ship with oil.

Libya's government has threatened legal action against anyone involved in helping the rebels export oil. It has not made any allegations of wrongdoing by the captain, by ZAD or Anazi.

ZAD's Anazi denied involvement in any plan to help the rebels sell oil. He declined to comment on Baig's contract and did not respond to multiple requests for further comment on the ownership and operations of the vessel.

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In a contract seen by Reuters dated February 22, 2014, Anazi is named as selling the tanker through a company called Morning Glory International Inc to a Libyan buyer.

On Tuesday Libyan rebels released a statement saying an individual still aboard the vessel had bought the ship, without revealing from whom. They accused the United States of "piracy" for raiding the ship.

It is not clear if the Morning Glory was Anazi's to sell, and he did not reply to requests for comment.

An archived page on ZAD Group's website shows an undated press release announcing "the procurement" of the vessel. But Sharjah-based Sea Pride Shipping said last week it was the owner, though it had not been operating the tanker since 2011.

It said it had started legal proceedings against Saud Shipping, which it said had refused to return the vessel.

"Sea Pride Shipping is very happy that the vessel has been seized," the company said in a statement on Monday, issued by a spokesman for a firm controlled by the Al Sari family.

Two members of the Al Sari family in the United Arab Emirates are the directors of Sea Pride Shipping. The Al Sari family controls the FAL Group, whose oil trading arm, FAL Oil Co, was sanctioned by Washington in 2012 for allegedly selling refined petroleum to Iran, which it denies.

Another FAL company, FAL Shipping, continued to get insurance cover for the Morning Glory until last month, the vessel's recent insurer said.

"According to our records, FAL Shipping Co Ltd was our insured member until February 27, 2014," said Anders Leissner of Swedish Club.

However, he said the insurance cover ended at that point because FAL Shipping sold the vessel to an unknown entity.

The spokesman for the Al Sari family-controlled company declined to comment on the Morning Glory's insurance or whether it had been sold.

Libya has said it believes the owner is an unnamed Saudi company.

TAKEN HOSTAGE

Public ship tracking data indicates that the tanker's position was not broadcast between January 2013 and last month, when it reappeared on February 28 and entered the Suez Canal en route to eastern Libya.

It was Captain Baig, having boarded the vessel in Eritrea in November, who took it through the Suez Canal, his brother-in-law Ayaz Malik said by phone from Karachi.

After passing through the Suez Canal, Baig was ordered by ZAD's Anazi to stop outside the Libyan port of Es Sider, Malik said. Armed rebels then sailed out from the port and boarded the ship, forcing the crew to dock and load it with oil.

"My husband and the crew have been held hostage by the rebels," Baig's wife, Qurat Noman Baig, told Reuters from Karachi.

"He did not want to dock at the Libyan port, but the rebels came on board and forced the crew at gun point to load the oil."

Reuters has not been able to independently confirm this account.

Despite warnings from Tripoli that the ship would be bombed if it left Es Sider, it sailed out of the port on March 11 under fire from the lightly armed Libyan navy.

Baig subsequently received directions from Anazi to head towards Greece, his brother-in-law Malik said, and shortly afterwards the U.S. seized the vessel.

A Cypriot police source said two Israelis and a Senegalese who flew into Cyprus by Learjet and took a charter vessel toward the tanker were detained for questioning on Saturday on suspicion of attempting to buy the cargo, which Libya considers stolen.

The source said the men, two of whom had diplomatic passports - one from Senegal and one from a central African country - were freed after a court declined to issue an arrest warrant and the men then left for Tel Aviv.

(Reporting by Ulf Laessing, Jonathan Saul, Steve Stecklow, Lin Noueihed and David Sheppard; Additional reporting by Jack Kim in Seoul and Humeyra Pamuk in Ankara; Writing by David Sheppard; Editing by Will Waterman)