*Seized American weapons were sold to UAE in 2008
The United States said Saturday it was looking into a report that American anti-tank missiles were found by forces loyal to Libya's unity government at a captured rebel base.
The New York Times reported Friday that four Javelin missiles were found at a base used by men under the command of Khalifa Haftar, a strongman who has waged a months-long offensive against Libya's internationally recognised government based in Tripoli.
Markings indicate the missiles were first sold to the United Arab Emirates.
"We take all allegations of misuse of US origin defence articles very seriously. We are aware of these reports and are seeking additional information," a State Department spokesperson said on condition of anonymity.
"We expect all recipients of US origin defence equipment to abide by their end-use obligations."
The missiles were apparently discovered earlier this week when forces loyal to the Government of National Accord recaptured the strategic town of Gharyan in a surprise attack, seizing the main supply base for Haftar's Tripoli offensive.
The New York Times reported that markings on the missiles indicated they had been sold to the UAE, a US ally, in 2008.
If they were then sold or transferred to Haftar, that would violate both the terms of the sale and a UN arms embargo on Libya, the report said.
The UAE, Egypt and Saudi Arabia are seen as key supporters of Haftar.
The State Department official said Washington supports the efforts of UN special envoy to Libya Ghassan Salame "to help avoid further escalation and chart a path forward that provides security and prosperity for all Libyans."
"We call on all parties to rapidly return to UN political mediation, the success of which depends upon a ceasefire in and around Tripoli," the US official said.
Hundreds of people have been killed and tens of thousands displaced in the offensive on Tripoli, while diplomatic efforts to revive political talks have foundered.
A report from Tripoli adds: Officials showed journalists weapons they said had been seized, among them sophisticated US-made Javelin anti-tank missiles.
They said they also captured some 150 prisoners.
UN reports have previously said that the UAE and Egypt have been arming Haftar's Libya National Army (LNA) since 2014, but details have been unclear.
Oded Berkowitz, Israeli security analyst and deputy chief intelligence officer of the MAX consultancy, said it was the first time that Javelins had been sighted in the Libya conflict.
"The weapons themselves are highly advanced but wouldn't be a game changer in Libya," he said. "The real political game changer is the fact that advanced US systems were delivered to a third party, and this may push the US to oppose the UAE and their support for the LNA."