TUNIS (Reuters) - Emirati assistance that violates a U.N. arms embargo has significantly boosted air power for forces loyal to Libyan commander Khalifa Haftar, a report by U.N. investigators published on Friday said.

Air power has helped Haftar’s eastern-based Libyan National Army (LNA) gain the upper hand since last year in Libya’s conflict between rival groups vying for power.

The panel of experts which reports on violations of U.N. sanctions across Libya said Haftar’s forces had received aircraft as well as military vehicles from the United Arab Emirates, and had built up an air base at Al Khadim.

The annual U.N. report provides rare detail on the level of outside intervention in Libya, where foreign backing for rival armed camps is widely seen as having exacerbated conflict.

Friday’s report said there had been a general increase in direct foreign support to armed factions in Libya, breaching a U.N. arms embargo imposed during the country’s 2011 uprising and tightened in 2014.

Much of the section on recent transfers of materiel or other assistance was taken up by the development of the LNA air force and reports of UAE assistance.

“The United Arab Emirates have been providing both material support and direct support to the LNA, which have significantly increased the air support available to the LNA,” it said.

The panel said its requests for information from the UAE had received no response.

Competition for power and wealth between broad and shifting coalitions of armed groups has thrown Libya into turmoil over the past six years. A collection of Islamist-leaning militias took control of the capital, Tripoli, in 2014, installing a self-declared government as their opponents set up a rival administration in the east.

The eastern government is aligned with Haftar, who has close relations to the UAE and Egypt and has rejected a third, U.N.-backed Libyan government that moved to Tripoli in March 2016. Haftar’s self-styled Libyan National Army has extended its control over towns, military bases and oil facilities in eastern and central Libya since last year. Air power has played a key role in those advances, analysts say.

The U.N. report included satellite imagery of Al Khadim air base, about 105 km (65 miles) east of Benghazi, between July 2014 and March 2017, showing a gradual build-up of infrastructure and aircraft, including drones “most probably” operated by the UAE.

The U.N. panel said it received information that attack helicopters were delivered to the LNA in April 2015. One Mi-24p helicopter was traced back to Belarus, which confirmed it had delivered four of the aircraft to the UAE in 2014.

It also published a photo of an AT-802i single engine plane which it said was based in eastern Libya. The plane, originally designed for agricultural or firefighting use, was repurposed in the United States for counter-insurgency and sold to the UAE, the report said.

The panel said it had confirmed a delivery of 93 armored personnel carriers and 549 armored and non-armored vehicles to the LNA in the eastern city of Tobruk in April 2016. The personnel carriers likely included Panther T6 and Tygra models, both made by companies based in the UAE, the report said, and were delivered by ship from Saudi Arabia.

It said it had received information on further large deliveries of Toyota pick-up trucks and armored 4x4 cars to Tobruk in January and April 2017, on a ship that had passed through Port Said in Egypt.