* Chinese ship surveyed Vietnamese oil blocks - U.S.
think-tanks
* One surveyed block licensed to Spanish energy firm Repsol
* Chinese ship 'threatened' rig operated by Russia's Rosneft
* Both China and Vietnam ask for sovereignty to be respected
* Vietnam prime minister tells coast guard to be 'ready to
fight'
(Adds Chinese foreign ministry comment, paragraph 19)
By James Pearson and Khanh Vu
HANOI, July 17 (Reuters) - Vietnamese and Chinese ships have
been embroiled in a weeks-long standoff near an offshore oil
block in disputed waters of the South China Sea, which fall
within Vietnam's exclusive economic zone, two Washington-based
think-tanks said on Wednesday.
China's U-shaped "nine-dash line" marks a vast expanse of
the South China Sea that it claims, including large swathes of
Vietnam's continental shelf where it has awarded oil
concessions.
The Haiyang Dizhi 8, a ship operated by the China Geological
Survey, on Monday completed a 12-day survey of waters near the
disputed Spratly Islands, according to separate reports by the
Center for Strategic and International Studies (CSIS) and the
Center for Advanced Defense Studies (C4ADS)
One of the oil blocks it surveyed is licensed by Vietnam to
Spanish energy firm Repsol REP.MC , which was forced last year
and in 2017 to cease operations in Vietnamese waters because of
pressure from China. As the Haiyang Dizhi 8 conducted its survey, nine Vietnamese
vessels closely followed it. The Chinese ship was escorted by
three China Coast Guard vessels, according to data from Winward
Maritime, compiled by C4ADS.
In a separate incident days earlier, the China Coast Guard
ship Haijing 35111 manoeuvred in what CSIS described as a
"threatening manner" towards Vietnamese vessels servicing a
Japanese-owned oil rig, the Hakuryu-5, leased by Russian state
oil firm Rosneft ROSN.MM in Vietnam's Block 06.1, 370 km (230
miles) southeast of Vietnam.
That block is within the area outlined by China's "nine-dash
line". A series of dashes on Chinese maps, the line is not
continuous, making China's claims often ambiguous.
Last year, Reuters exclusively reported that Rosneft Vietnam
BV, a unit of Rosneft, was concerned that its drilling in Block
06.1 would upset China. "On July 2 the vessels were leaving the Hakuryu-5 when the
35111 manoeuvred between them at high speed, passing within 100
metres of each ship and less than half a nautical mile from the
rig," CSIS said in its report.
It was not clear on Wednesday if any Chinese ships were
still challenging the Rosneft rig.
In 2014, tension between Vietnam and China rose to its
highest levels in decades when a Chinese oil rig started
drilling in Vietnamese waters. The incident triggered boat
rammings by both sides and anti-China riots in Vietnam.
'READY TO FIGHT'
In response to reports of this month's standoff, which first
emerged on social media, Chinese foreign ministry spokesman Geng
Shuang said on July 12 that China's position on the South China
Sea was "clear and consistent".
"China resolutely safeguards its sovereignty in the South
China Sea and maritime rights, and at the same time upholds
controlling disputes with relevant countries via negotiations
and consultations," Geng said, without elaborating.
On Tuesday, Vietnam's foreign ministry released a statement
in response to unspecified "recent developments" in the South
China Sea.
"Without Vietnam's permission, all actions undertaken by
foreign parties in Vietnamese waters have no legal effect, and
constitute encroachments in Vietnamese waters, and violations of
international law," foreign ministry spokeswoman Le Thi Thu Hang
said.
Neither statements confirmed or elaborated on the standoff.
Neither Rosneft nor Repsol immediately responded to an
emailed request from Reuters for comment.
In a new statement on Wednesday, China's foreign ministry
spokesman Geng acknowledged that there had been an incident with
Vietnam.
"We hope the Vietnam side can earnestly respect China's
sovereignty, rights, and jurisdiction over the relevant waters,
and not take any actions that could complicate the situation,"
Geng told a regular news conference.
On July 11, as China was conducting its survey of the
blocks, Vietnam's prime minister, Nguyen Xuan Phuc, visited the
headquarters of the Vietnam Coast Guard in Hanoi.
State media did not mention the incident, but showed Phuc
speaking to sailors on board vessels via a video link.
Phuc told the sailors to "stay vigilant and ready to fight"
and to be aware of "unpredictable developments", the Vietnam
Coast Guard said in a statement on its website.
On the same day, Vietnam's national assembly chairwoman,
Nguyen Thi Kim Ngan, met her Chinese counterpart, Li Zhanshu, in
Beijing, China's Xinhua news agency reported.
The two officials agreed to "jointly safeguard peace and
stability at sea", Xinhua said.