Paris (AFP) - France is increasing its military presence in the Indo-Pacific region, sending warships through the South China Sea and planning air exercises to help counter China's military build-up in disputed waters.

In late May, the French assault ship Dixmude and a frigate sailed through the disputed Spratly Islands and around a group of reefs that China has turned into islets to push back against Beijing's claim to own most of the resource-rich South China Sea.

"Our patrol involved passing close to these islets to obtain intelligence with all the sensors it is possible to use in international waters," the Dixmude's commanding officer, Jean Porcher, told reporters in a video interview.

Writing in The Wall Street Journal, a researcher from the Hudson Institute think-tank who was onboard, said that "several Chinese frigates and corvettes" tailed the French vessels.

Porcher said the ship maintained "cordial" radio contact with Chinese military vessels, "which were present in the area until we left".

So far the United States has taken the lead in confronting China over its territorial claims in the South China Sea, which are contested by several neighbours, particularly Vietnam.

But France, which along with Britain is the only European nation to regularly send its navy into the region, has also waded into the dispute, sending its ships into the South China Sea three to five times a year.

In August, the airforce will stage its biggest-ever exercises in southeast Asia as part of a strategy to mark France's presence in a region that is home to 1.5 million French citizens in the country's overseas territories.

Three Rafale fighter jets, one A400M troop transporter and a C135 refuelling tanker will fly from Australia to India, with several stop-offs along the way.

The sea and air operations follow a visit by President Emmanuel Macron last month to Australia, where he spoke of the need to protect the Indo-Pacific region from "hegemony" -- a veiled reference to Beijing's growing might.

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He stressed that France, which will be the last country in the EU after Britain leaves the bloc to have territories in the Pacific, did not want to antagonise China.

But a "strong Indo-Pacific axis" was needed to ensure respect for freedom of navigation and aviation in the region, he told Australian Prime Minister Malcolm Turnbull.

- Supporting arms customers -

Macron appears to be "realistically assessing the growing Chinese challenge", said Jonas Parello-Plesner, a researcher from the US-based Hudson Institute who was an observer on the recent French navy voyage.

"This is a welcome change from his predecessors, who were enthralled by the business and investment opportunities in China," he wrote in The Wall Street Journal.

But France had already began to push back against China's expansionism before Macron took power.

Since 2014, the navy has sailed regularly through the South China Sea as part of its stated bid to uphold a rules-based maritime order.

In 2016, then French defence minister Jean-Yves Le Drian (now the foreign minister) called on other European navies to develop a regular and visible presence in the South China Sea.

Besides protecting navigation, France has cited the need to defend the interests of its citizens scattered across five French territories in the Pacific, including New Caledonia and French Polynesia.

"This region is also our home," current Defence Minister Florence Parly said during a visit to Singapore in early June.

Valerie Niquet, an expert on the Asia-Pacific region at the Foundation for Strategic Research in Paris, said France's growing assertiveness showed the US was no longer the only Western power "getting involved in the area".

"Faced with China the US obviously plays the main deterrent role, but it's not pointless or trivial for a power like France, a permanent member of the (UN) Security Council, to take a firm, principled position and carry out concrete actions," she said, predicting that it would "marginalise China's position a little bit more".

Analysts point to another factor underpinning France's growing activism in the Indo-Pacific region: the need to show buyers of French arms that Paris has their back.

In 2016, India agreed buy 36 Rafale fighter jets and Australia signed a deal worth 50 billion Australian dollars ($37 billion, 31 billion euros) for 12 next-generation French submarines.

"That is also doubtlessly pushing France to be a lot firmer on subjects that, up until recently, were broached with great care," Niquet said.