Military tensions are re-emerging in the South China Sea, where Australian warship HMAS Parramatta has recently conducted exercises with the US Navy.

Key points: Naval exercises were conducted with US forces in the disputed waters

Tensions in the region are re-emerging, with China increasing its presence

Defence says Australia has a "robust" policy of engagement in the region

In a tweet published early on Wednesday morning, the US Navy confirmed three of its warships had transited the South China Sea "in support of security and stability in the Indo-Pacific region".

The Defence Department said "over the past few days", the ANZAC-class frigate exercised with the US ships as they passed through the contested region.

"HMAS Parramatta has been undertaking an extended deployment throughout South and South-East Asia for the last two months, to help strengthen the stability and security of the region," a Defence spokesperson said.

Defence experts believe Australia's participation in the military drills alongside the US would have been planned months in advance.

But the show of force comes at a significant time, as other nations express growing concerns with China's expansion in the region

The manoeuvring in the South China Sea was announced days after China bolstered its presence by setting up two administrative bodies on islands in the disputed water, dubbing the area "its youngest city".

In March, Beijing also launched two new research stations on artificial reefs in territory claimed by the Philippines and others.

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The Defence spokesperson said that during their time in the region, Australian and US forces went through exercises on the water together.

"During the passage exercises, the ships honed interoperability between Australian and US navies, including replenishment-at-sea, aviation operations, maritime manoeuvres and communications drills," the spokesperson said.

The department also insisted "Australia has maintained a robust program of international engagement with countries in and around the South China Sea for decades".

American Aircraft carrier USS Theodore Roosevelt, which had been sailing in the South China Sea earlier this year, was recently struck by an outbreak of the coronavirus that killed one sailor and infected hundreds of others.

Last year, HMAS Parramatta was part of an Australian Task Group that was closely tracked by the Chinese military as it made its way through the Indo-Pacific region.

Despite the emergence of the coronavirus pandemic in January, Australian officials have been closely watching as Beijing ramps up its activities in the strategically important South China Sea.

Earlier this month, Vietnam lodged an official protest with Beijing after the sinking of a Vietnamese fishing boat it said had been rammed by a China Coast Guard vessel near the Paracel Islands.