Libya threatened yesterday to bomb a North Korean-flagged tanker at an oil terminal in the restive east if it does not leave port, saying it was loading illegally.
Separatist militants blockading the Sidra facility in eastern Libya attempted to load crude aboard the ship the Morning Glory in the latest challenge to central government control.
The self-proclaimed government of Cyrenaica in the east, the political wing of the separatists, said oil exports from Sidra had now begun.
"We announce to Libyans and to the whole world that we have begun exporting oil," said Rabbo al-Barassi, who heads the Cyrenaica executive bureau formed in August by federalist activists.
"We are not defying the government or the congress [parliament]. But we are insisting on our rights," he said.
Protesters at eastern oil ports are demanding a restoration of the autonomy the eastern region was granted in the first decade after Libya's independence in 1951.
They have also accused the authorities of corruption and are demanding a more equitable distribution of oil revenues.
Deputy Defence Minister Khaled al-Sherif said a "crisis committee" of government officials and lawmakers had issued an ultimatum for the oil tanker to leave Libyan territorial waters.
"If the ship doesn't comply, it will be bombed by the air force or intercepted at sea by the navy," Sherif warned.
A member of parliament and committee member said the deadline expired without any action being taken.
Washington's envoy to Tripoli warned on Twitter that any cargo deemed to have been loaded illegally would face international sanction.
"Companies that engage in illicit trade with separatist groups in Libya risk liability in multiple jurisdictions," US ambassador Deborah Jones tweeted. "The only entities authorised to sell Libya's oil are the Libyan National Oil Corp, its subsidiaries JV partners," she added.
Acting Oil Minister Omar Shakmak denounced the move as an "act of piracy".
"This is a violation of national sovereignty. It is up to the defence ministry to deal with this ship," he said, without elaborating.
Yesterday's incident was the latest in a stand-off between the government and militants over exports, which are the principal source of revenue for the North African country.
Oil installation guards launched the blockade of key petrol sites last July, initially over price rises but later also to call for autonomy for Cyrenaica, cradle of the 2011 revolt that toppled Muammar Gaddafi.
In January, the navy prevented two tankers from docking in Sidra to take on crude.