French authorities have opened an investigation into the leaking of a classified military note which revealed French weapons are being used by the United Arab Emirates and Saudi Arabia in Yemen, sources told AFP on Wednesday.

The note details the use of weapons -- including tanks, artillery and military ships -- in the war against Huthi rebels.

The use of French weapons in Yemen appears to contradict previous public statements from France's government.

The classified 15-page note from the French military intelligence service, published in April by new investigative media outlet Disclose, concluded that the UAE and Saudi Arabia had deployed French weaponry.

The note -- provided to the government in October 2018, according to Disclose -- said 48 CAESAR artillery guns manufactured by the Nexter group were being used along the Saudi-Yemen border.

Leclerc tanks, sold in the 1990s to the UAE, have also been used, as have Mirage 2000-9 fighter jets, while a French missile-guiding technology called DAMOCLES might have been deployed, according to the assessment.

Cougar transport helicopters and the A330 MRTT refuelling plane have also seen action, and two French ships are serving in the blockade of Yemeni ports which has led to food and medical shortages, the DRM military intelligence agency concluded.

Under pressure for years by rights groups over the sales, the Paris government has always insisted that the arms are only used in defensive circumstances to deter attacks by the Huthis.

The investigation into the "compromise of national defence secrecy" was launched by prosecutors on December 13 last year after a complaint by the armed forces ministry, a judicial source said.

France's domestic intelligence agency, the DGSI, is leading the inquiry, which concerns the compromise of information involving a government employee and a third party, the source said.

- 'Attack on press' -

France, the third-biggest arms exporter in the world, counts Saudi Arabia and the UAE as loyal clients in the Middle East and has resisted pressure to stop the arms trade -- unlike Germany, which has suspended sales.

Rights groups have regularly accused Paris of being complicit in alleged war crimes committed in Yemen where around 10,000 have died and millions have been forced to the brink of starvation.

The UAE and Saudi Arabia, which own billions of dollars' worth of weapons bought from the United States, France and Britain, intervened in 2015 to support the Yemeni government against Huthi rebels, which are backed by rival Iran.

The UN calls the situation in the war-torn country the world's worst humanitarian crisis. Experts have concluded that all the warring parties have violated international humanitarian law.

"The confidential documents revealed by Disclose and its partners are of major public interest, that bring to the attention of citizens and their representatives what the government wanted to conceal," said an editorial for Disclose and its partners.

Disclose worked with several media organisations including public broadcaster France Info, online brand Mediapart and Franco-German television channel Arte.

The founder of Disclose, Geoffrey Livolsi, told AFP that at least three journalists who took part in the investigation have been called in for a hearing conducted by the DGSI next month.

"This judicial investigation has only one objective: to know the sources that allowed us to do our job. It is an attack on the freedom of the press and the protection of the sources of journalists," Livolsi said.

French Armed Forces Minister Francoise Parly said during an interview in January on the France Inter radio station: "I'm not aware that any (French) arms are being used in this conflict."