Tripoli - The Libyan navy moved on Monday to stop a North Korean ship from leaving a rebel-held port loaded with oil, as the US accused the separatists of theft and warned any buyers could face sanctions.
Navy ships were deployed to block the "Morning Glory" from leaving port, after Culture Minister Amin al-Habib said on Sunday the tanker would be "turned into a pile of metal" if it tried to set sail with its cargo.
The defence ministry has also deployed the air force to "deal with the tanker", the official Lana news agency reported.
The United States said it was "deeply concerned" over the loading of the "illicitly obtained" oil.
"This action is counter to law and amounts to theft from the Libyan people," State Department spokeswoman Jen Psaki said in a statement.
"The oil belongs to the Libyan National Oil Company and its joint venture partners," Psaki said, noting the partners include US companies.
"Any oil sales without authorisation from these parties places purchasers at risk of exposure to civil liability, penalties and other possible sanctions in multiple jurisdictions."
Rebels at the Al-Sidra oil terminal in eastern Libya spent the weekend loading oil onto the tanker, ignoring Prime Minister Ali Zeidan's threats to bomb the ship and Oil Minister Omar Shakmak's accusation of "piracy".
The ship can carry up to 350 000 barrels of crude.
The separatists are former rebels who have turned against Libya's interim authorities after toppling veteran dictator Muammar Gaddafi in the north African country's 2011 uprising.
They have been blockading oil terminals in eastern Libya that they had been entrusted with guarding, demanding autonomy and a share in lucrative oil revenues.
Zeidan told a news conference Saturday that the attorney general had given the order for the ship to be stopped.
"All parties must respect Libyan sovereignty. If the ship does not comply, it will be bombed," he said.
Zeidan said the authorities had told the vessel's captain to leave Libya's waters, but added that armed gunmen on board were preventing him from setting sail.
A spokesperson for the self-proclaimed government of Cyrenaica in the east, the separatists' political wing, said Saturday that oil exports from Al-Sidra had begun.
"We are not defying the government or the Congress [parliament]. But we are insisting on our rights," said Rabbo al-Barassi, who heads the Cyrenaica executive bureau formed in August.
The crisis erupted in July, when security guards at key terminals shut them down, accusing the authorities of corruption and demanding a more equitable distribution of oil revenues.
The situation has become more complicated as self-rule activists have insisted on the right to export.
Oil is a key source of revenue for Libya and following the blockade of terminals production plunged to about 250 000 barrels per day from 1.5 million barrels.