France has said some of its missiles were found at a Libyan base used by forces loyal to the military strongman Khalifa Haftar – an embarrassing admission that raises new questions about its role in the conflict.

Confirming a report in the New York Times, the French defence ministry said it had purchased the US-made Javelin missiles that were subsequently discovered at a camp south of Tripoli.

It denied supplying them to Haftar, which would have been in breach of a UN arms embargo, saying French forces operating in Libya lost track of them after they were judged to be defective.

“Damaged and out of use, these weapons were being temporarily stocked in a warehouse ahead of their destruction,” it said. “They were not transferred to local forces.”

The anti-tank missiles were seized when forces loyal to the UN-recognised government in Tripoli overran a pro-Haftar base in Gharyan, 60 miles south of Tripoli. Three of them were shown to journalists on 29 June alongside Chinese-made shells bearing the markings of the United Arab Emirates.

Claudia Gazzini, senior Libya analyst at the International Crisis Group, an NGO, said the town of Gharyan had in the past housed facilities for obsolete weapons. She said there were unanswered questions about whether French troops were present when the base was overrun.

“The French need to clarify in greater detail,” she said. “The open question is whether or not they are actively supporting Haftar’s forces in their offensive on Tripoli.”

Haftar’s opponents have said he is a dictator in the making, but he is backed by some western and many neighbouring countries as a bulwark against Islamist groups.

On 4 April he launched an offensive on the Libyan capital seeking to overthrow the government of the prime minister, Fayez al-Sarraj.

The Libyan conflict has drawn in a range of regional and international actors and the country is awash with foreign weaponry despite the UN embargo.

France under Emmanuel Macron has publicly denied taking sides in the conflict and has called for the embargo to be enforced.