Vietnam demands 'immediate withdrawal' of China ship in disputed sea

Vietnam on Thursday called for the "immediate withdrawal" of a Chinese ship in the South China Sea, as the standoff over the disputed waters intensified.

Beijing last week issued a new call for Hanoi to respect its claims to the resource-rich region -- which have historically been contested by Vietnam as well as Taiwan, the Philippines, Malaysia and Brunei.

Hanoi responded by saying it had sent several messages to Beijing insisting that a Chinese survey ship vacate its waters, and doubled down Thursday with new demands for the vessel's removal.

"Vietnam has had several appropriate diplomatic exchanges... requesting immediate withdrawal from Vietnam's exclusive economic zone," a foreign ministry spokeswoman told reporters, while refusing to disclose the ship's precise location.

"Vietnam resolutely and persistently protects our sovereign rights... by peaceful means on the basis of international laws," Le Thi Thu Hang added.

The ship, owned by the government-run China Geological Survey, begun research around the contested Spratly Islands on July 3, according to the US-based Center for Strategic and International Studies (CSIS).

Before it was spotted, a Chinese coast guard vessel also patrolled near Vietnamese supply ships in a "threatening manner", CSIS said.

China has not confirmed the presence of its ships in the area.

Beijing invokes its so-called nine-dash line to justify its apparently historic rights to the waterway, and has previously built up artificial islands as well as installed airstrips and military equipment in the region.

The line runs as far as 2,000 kilometres (1,200 miles) from the Chinese mainland to within a few hundred kilometres of the Philippines, Malaysia and Vietnam.

In 2014 Beijing moved an oil rig into waters claimed by Hanoi, sparking deadly, anti-China protests across Vietnam.

The latest stand-off in the Sea prompted a swift rebuke from the United States over the weekend, calling for an end to China's "bullying behaviour".

"China's repeated provocative actions aimed at the offshore oil and gas development of other claimant states threaten regional energy security," the US State Department said Saturday.

The United States has long called for freedom of navigation in the South China Sea, and on Thursday said it sailed a warship through the Taiwan Strait.