TRIPOLI, July 22 (Xinhua) -- The United States special representative called on Sunday for "immediate and unconditional release" of foreign engineers kidnapped by unidentified gunmen in an oil field in southern Libya.

Deputy Special Representative of the UN Secretary-General for Political Affairs (DSRSG-Political) Stephanie Williams made her remarks during a meeting with the Chairman of the state-owned National Oil Corporation (NOC) Mustafa Sanalla in Libyan capital Tripoli.

"Williams condemned the hijacking of oil workers in Sharara oil fields and called for their immediate and unconditional release," the UN Mission in Libya said in a statement.

In mid July, unknown gunmen kidnapped four engineers, including three Libyans and one Romanian, working in Sharara oil field in southern Libya.

Two Libyan engineers were released shortly afterwards, while the remaining two are still held captive.

"The DSRSG-Political reiterated that Libya's wealth belongs to the Libyan people and underscored that the NOC is the sole internationally recognized and legitimate authority for oil and gas in Libya," the statement said.

Sharara is Libya's largest oil field, with a production of almost 270,000 barrels of crude oil per day, nearly one quarter of the country's daily oil output.

In November 2017, an unidentified armed group kidnapped four foreign workers, including three Turks and a German, who were working at the power station in Obari, 1,100 km south of Tripoli.

The workers were released two weeks ago after tribal mediation with the kidnappers.

Following the 2011 uprising that toppled former leader Muammar Gaddafi's government, Libya has been suffering escalating violence and insecurity, as well as political division.