Senators Bob Menendez, Ed Markey, Patrick Leahy and Brian Schatz have written to U.S. Secretary of State Mike Pompeo, asking him to accord high priority to China’s maritime aggression in the South China Sea at the ASEAN Regional Forum to be held Friday in Bangkok, Thailand.

Earlier this month, China sent out its oil survey vessel Haiyang Dizhi 8 and escorts to Vietnamese waters near the Vanguard Bank in the south of the South China Sea, which Vietnam calls the East Sea. China’s actions infringed on Vietnam’s exclusive economic zones (EEZ) and continental shelf, Vietnam’s Foreign Ministry spokeswoman Le Thi Thu Hang said last Thursday, repeating demand that the Chinese ships leave Vietnamese waters.

The U.S. senators urged Pompeo on Monday to "ensure that China’s aggressive and expansionist behavior in the South China Sea is a top priority" in discussions at the forum.

China’s assertive behavior in the EEZ of other states, its use of reclaimed and militarized artificial features as platforms for coercion, its decision to ignore the Permanent Court of Arbitration ruling against its territorial claims, and its efforts to pressure ASEAN to negotiate a restrictive Code of Conduct all "deserve greater U.S. attention, leadership and cooperation with our allies and partners," they said.

"A South China Sea where international law is respected, freedom of navigation is ensured, commerce flows freely, multilateral regional organizations are central, and regional countries are not subject to coercion is crucial to American interests in the Indo-Pacific," the senators wrote.

"China’s intimidation, coercion, rejection of peaceful diplomatic arbitration, and threats of the use of force over the past several years represent a serious challenge to those interests."

While the senators welcomed the U.S. administration highlighting China’s militarization of the South China Sea as well as the regular and routine conduct of freedom of navigation assertions, they believed that "much more is needed" to counter China’s activities and impede its drive to operate with impunity in the South China Sea.

"This challenge requires a fully articulated and comprehensive strategy and a regional consensus with allies and partners, with ASEAN at the center of those efforts," they said.

The meeting in Bangkok, they said, should be an opportunity to begin to forge such a consensus "to protect the rights of U.S. allies and partners under the United Nations Convention on the Law of the Sea, end Chinese infringement of the legitimate rights of other coastal states, build respect for international law and institutions, and counter China’s efforts to undermine a free and open Indo-Pacific."

It is not too late to hold China to account for its behavior, and to deter further Chinese aggression in the maritime domain."

Monday’s letter was the third public statement made by U.S. officials against China's activities in the South China Sea in the past 10 days.

The U.S. Department of State had said July 20 that it was concerned by reports of China’s interference with Vietnam and other countries' oil and gas activities.

It called Chinese acts "bullying," saying that China’s reclamation and militarization of disputed outposts in the waterway, including the use of maritime militia to intimidate, coerce, and threaten other nations, undermined peace and security in the region.

On July 26, Representative Eliot L. Engel, Chairman of the House Committee on Foreign Affairs, said in a statement that "China’s recent aggression in the South China Sea is a disturbing demonstration of a country openly flouting international law."

The presence of the Chinese survey ship in Vietnamese waters has garnered international attention.

Experts said China was trying to turn Vietnamese territory into a disputed area to advance its superpower plans, but the actions could erode bilateral and regional trust and affect domestic opinion.

China claims almost the entire South China Sea, including waters close to Taiwan and Southeast Asian countries Brunei, Indonesia, Malaysia, the Philippines and Vietnam.

The ASEAN Regional Forum in Bangkok is part of the 52nd ASEAN Foreign Ministers’ Meeting and Post Ministerial Conferences running from Monday to Saturday.

Delegates from 30 countries are attending the Foreign Minister’s Meeting. The Vietnamese delegation is led by Deputy Prime Minister and Foreign Minister Pham Binh Minh.