HANOI (Reuters) - A Chinese ship embroiled in a standoff with Vietnamese vessels last year has returned to waters near Vietnam as the United States accused China of pushing its presence in the South China Sea while other claimants are pre-occupied with the coronavirus.

Vietnamese vessels last year spent months shadowing the Chinese Haiyang Dizhi 8 survey vessel in resource-rich waters that are a potential global flashpoint as the United States challenges China’s sweeping maritime claims.

On Tuesday, the ship, which is used for offshore seismic surveys, appeared again 158 km (98 miles) off Vietnam’s coast, within its exclusive economic zone (EEZ), flanked by at least one China Coast Guard vessel, according to data from Marine Traffic, a website that tracks shipping.

At least three Vietnamese vessels were moving with the Chinese ship, according to data issued by the Marine Traffic site.

Vietnam was closely monitoring activity in the South China Sea, its Ministry of Foreign Affairs said.

China’s foreign ministry said the ship was not doing anything unusual.

“The Chinese survey ship was conducting normal activities in waters administered by China,” ministry spokesman Zhao Lijian told a daily news briefing in Beijing on Wednesday.

The presence of the Haiyang Dizhi 8 in Vietnam’s EEZ comes towards the scheduled end of a 15-day nationwide lockdown in Vietnam aimed at curbing the spread of the coronavirus.

It also follows the sinking of a Vietnamese fishing boat near islands in the disputed waters this month, an act that drew a protest from Vietnam and accusations that China had violated its sovereignty and threatened the lives of its fishermen.

The United States, which last month sent an aircraft carrier to the central Vietnamese port of Danang, said it was “seriously concerned” about China’s reported sinking of the vessel.

“We call on the PRC to remain focused on supporting international efforts to combat the global pandemic, and to stop exploiting the distraction or vulnerability of other states to expand its unlawful claims in the South China Sea,” the U.S. State Department said in a statement, referring to China.

But Zhao said some U.S. officials had been using the South China Sea issue to smear China.

‘BASELESS’

The Philippines, which also has disputed claims in the South China Sea, has raised its concerns too.

On Saturday, China’s Global Times, published by the official People’s Daily newspaper of China’s ruling Communist Party, said Vietnam had used the fishing boat incident to distract from its “ineptitude” in handling the coronavirus.

Helped by a mass quarantine and aggressive contact-tracing, Vietnam has recorded 267 cases of the novel coronavirus and no deaths. Nearly 122,000 coronavirus tests have been carried out in Vietnam.

China and Vietnam have for years been at loggerheads over the potentially energy-rich waters, called the East Sea by Vietnam.

China’s U-shaped “nine-dash line” on its maps marks a vast expanse of the waters that it claims, including large parts of Vietnam’s continental shelf where it has awarded oil concessions. Malaysia and Brunei claim some of the waters that China claims to the south.

During the standoff last year, at least one China Coast Guard vessel spent weeks in waters close to an oil rig in a Vietnamese oil block, operated by Russia’s Rosneft, while the Haiyang Dizhi 8 conducted suspected oil exploration surveys in large expanses of Vietnam’s EEZ.

“The deployment of the vessel is Beijing’s move to once again baselessly assert its sovereignty in the South China Sea,” said Ha Hoang Hop, at the Singapore-based ISEAS-Yusof Ishak Institute.

“China is using the coronavirus distraction to increase its assertiveness in the South China Sea, at a time when the U.S. and Europe are struggling to cope with the new coronavirus.”