A senior US senator demands an investigation over reports that American-made weapons were found at a base of forces loyal to Khalifa Haftar, the East Libyan-based military commander, as reported by Anadolu Agency.
The UN-recognised Government of National Accord (GNA) said its forces found the weapons at a base they captured from Haftar's militia in the strategic town of Gharyan, south of the capital Tripoli, last week.
It said the seized weapons included four Javelin anti-tank missiles packed in wooden crates marked "armed forces of the United Arab Emirates."
In a letter to Secretary of State Mike Pompeo, Senator Robert Menendez of New Jersey, the top Democrat on the Foreign Relations Committee, voiced deep concern over the reports and said if the Emirates transferred the weapons, it would be a "serious violation" of US law.
"Such a transfer would also almost certainly be a violation of the UN arms embargo on Libya," said Menendez's letter.
"I understand that the State Department may have begun an investigation; if not, I demand that a full investigation be done immediately," he added.
Haftar's forces have been unsuccessful in seeking to capture Tripoli from the Government of National Accord in an offensive that began in April.
Libya has remained beset by turmoil since 2011, when a bloody NATO-backed uprising led to the ouster and death of long-serving President Muammar Gaddafi after more than four decades in power.
Since then, Libya's stark political divisions have yielded two rival seats of power, one in Tobruk led by Haftar and another in Tripoli, and a host of heavily armed militia groups.