It appears Beijing has made a dramatic tactical move, just days before Southeast Asian leaders gather in Bangkok for an annual summit to discuss important regional political, economic and social issues, by pulling out its oil survey vessel from Vietnamese-controlled waters in the disputed South China Sea.

A Reuters report, quoting marine data, said the Chinese survey vessel, Haiyang Dizhi 8, had left an area within Vietnam’s 200-mile exclusive economic zone, escorted by two Chinese ships, steaming towards China’s waters. It had been embroiled in a tense standoff with Vietnamese ships for more than three months.

It was first seen in Vietnamese-controlled waters in July, left briefly for Fiery Cross, an artificial island that China built in the Spratlys, but returned in August and remained there until late October.

Some commentators said it was an embarrassment to Xi Jinping, who has been resolute in pursuing Beijing’s claims on almost the entire South China Sea. The basis is a 1949 map showing the nine-dash-line surrounding the energy-rich waters. Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have conflicting claims on the strategic waterway where about $3 trillion in goods pass every year.

But China could just be avoiding a sensitive issue when the Association of Southeast Asian Nations (Asean) holds its annual summit this week in Bangkok. Asean’s dialogue partners, including the United States, China, Australia, Japan, India, New Zealand and South Korea are also expected to attend the gathering.

Washington and its allies usually take the occasion to criticize China’s island-building and increasing militarization in the South China Sea as well as urge Beijing to agree to a rules-based Code of Conduct and comply with the 2016 decision of the Permanent Court of Arbitration in The Hague.

Since 2013, there has been mounting pressure from Western countries, as well as China’s bitter rivals India and Japan, on the South China Sea, but this did not stop Beijing from completing seven man-made islands and building military facilities, including airfields and secured ports.

It continued the deployment of hundreds of vessels to the disputed sea, harassing vessels from rival claimant-states, particularly from Vietnam and the Philippines. In June, a Filipino fishing boat was rammed and sunk, leaving more than 20 crew on the waters until they were rescued by a Vietnamese fishing crew.

While Asean’s dialogue partners are ganging up on China, Beijing was more successful in dividing the 10-member regional bloc, which pride themselves to be on the driver’s seat in all regional political, economic and social initiatives.

Asean’s voice has been muted although it always comes up with joint statements on South China Sea, calling for restraint and dialogue and expressing concern over growing tensions as Beijing expands its military presence and influence in the waters.

Four years ago, two claimant-states – Vietnam and the Philippines – pressured China to adhere to international legal regimes as a responsible member of the international community. Within Asean, however, there had been a number of times a stronger statement to rebuke China was defeated because Beijing has a strong ally in Cambodia.

Asean works on consensus and one vote against a political action could spell disaster, like what happened in 2012 when the bloc failed to come up with a negotiated joint communique during the Asean Foreign Ministers’ Meeting in Phnom Penh. Cambodia blocked a text in the joint statement on Beijing’s militarization and island-building.

In Bangkok, Vietnam is the lone voice in the wilderness in opposing China, as the Philippines, under President Rodrigo Duterte, has softened and repaired its relations with Beijing, hoping to capture the huge China market as well as obtain much-needed investments, official development assistance and tourist arrivals.

Although China has been more successful in deflecting criticisms within Asean, it still hopes for a smooth and uneventful Asean Summit and lessen the noise from its critics and foes. Thus, it could have voluntarily pulled out its survey ship to remove a potential issue, which Hanoi could raise during the meeting.

In another Reuters report, Chinese Foreign Ministry spokeswoman Hua Chunying said the survey ship’s “work is presently complete.”

But Ha Hoang Hop of the International Institute for Strategic Studies told Reuters China’s withdrawal could be temporary and the ship would soon be back in the area.

“It’s very likely that China will send an oil rig to drill in the area where the Haiyang Dizhi 8 had conducted seismic surveys in Vietnam’s exclusive economic zone,” Hop said.

There is an emerging pattern of Chinese behavior in the South China Sea in terms of energy exploration and extraction. It seems Beijing wants to partner with Asean states in all oil-and-gas activities in the South China Sea, discouraging Southeast Asian countries, particularly claimant-states, from entering into joint ventures with other parties, like the Russians, Spanish, British and Americans.

“China doesn’t want any non-Asean companies to drill for oil in the South China Sea,” Hop, who is also a visiting senior fellow at the ISEAS-Yusof Ishak Institute in Singapore, told Reuters. “China is determined to pressure Vietnam to end joint oil exploration and production with foreign partners in the area.”

Vietnam has stopped a partnership with Spain and China has been sending coast guard ships in an oil bloc where Vietnam and Russia’s Rosneft were exploring oil and gas.

Rosneft is a company controlled by a close ally of Russian leader Vladimir Putin, Igor Sechin, the de facto No. 2 in the Russian government, who like Putin had been in the Russian state security agency.

Rosneft recently had an agreement with the Philippine state-owned oil company for petroleum trading, which is now under scrutiny after the deal was illegally entered into by the former head of the state-owned oil exploration company.

China is also discussing with the Philippines a proposed joint exploration in the Reed Bank, and a joint steering committee from the two countries’ foreign and energy ministries is expected to come up with a commercial deal by the end of the year.