KUALA LUMPUR--Malaysia called on Thursday for disputes over the South China Sea to be resolved by peaceful means, amid a standoff between Chinese and Malaysian vessels that a U.S. think tank said had been going on for months.

U.S. and Australian warships arrived in the South China Sea this week near an area where a Chinese government survey vessel, the Haiyang Dizhi 8, has been operating close to a drill ship under contract to Malaysian state oil company Petronas, regional security sources have said.

The standoff was the latest development in a series of targeted harassments by Chinese vessels of drilling operations in five oil blocks off the Malaysian coast in the past year, said Greg Poling, director of the Washington-based Asia Maritime Transparency Initiative (AMTI).

Since December, Chinese forces have been harassing supply ships servicing the West Capella, an oil exploration vessel operated by Petronas, Poling said.

Last week, the Haiyang Dizhi 8, accompanied by a Chinese coast guard vessel, entered Malaysia’s exclusive economic zone (EEZ) and began a survey close to where the West Capella was operating.

On Thursday, the Haiyang Dizhi 8 was still within Malaysia’s EEZ, about 337 kilometers off Borneo, data from ship tracking website Marine Traffic Showed.

Three U.S. warships and an Australian frigate conducted a joint exercise in the South China Sea this week, near the site of the West Capella’s operations, officials and security sources have said.

The area is near waters claimed by Vietnam, Malaysia and China, which claims most of the energy-rich South China Sea through a U-shaped “nine-dash line” on its maps not recognized by its neighbors.

China has denied reports of a standoff, saying the Haiyang Dizhi 8 was carrying out normal activities.

Malaysia on Thursday said it remained committed to safeguarding its interests in the South China Sea.

“While international law guarantees the freedom of navigation, the presence of warships and vessels in the South China Sea has the potential to increase tensions that in turn may result in miscalculations which may affect peace, security and stability in the region,” Foreign Minister Hishammuddin Hussein said in his first official remarks on the standoff.

Hishammuddin said Malaysia maintained “open and continuous communication” with all relevant parties, including China and the United States.

Petronas did not respond to requests for comment.

AMTI’s Poling said Petronas may pull out of the area eventually due to the Chinese presence. Spanish energy firm Repsol halted two Vietnamese drilling projects in 2017 and 2018 following pressure from China.

The United States has called on China to stop “bullying tactics” in the South China Sea and accused Beijing of pushing its presence in the disputed waters while other claimants are preoccupied with the coronavirus.