"Vietnam has made contact multiple times and requested that China withdraws its ships, and not engage in behavior that threatens security and peace in the region," Foreign Ministry spokeswoman Le Thi Thu Hang said at a press meet Thursday.

She said that Chinese ships have returned and seriously infringed on what is Vietnam’s exclusive economic zone (EEZ) and continental shelf under the United Nations Convention on the Law of the Sea (UNCLOS).

Hang was responding to questions about Vietnam’s actions upon Chinese oil survey vessel Haiyang Dizhi 8 and escorts returning to Vietnamese waters near the Vanguard Bank in the East Sea, internationally known as the South China Sea, on August 13.

The ship and its escorts had left the nation’s exclusive economic zone (EEZ) and continental shelf on August 7 after occupying Vietnamese sea territory for about a month. Vietnam had publicly condemned the vessels' return last Friday.

"Vietnam’s authorities continue to protect Vietnam’s sovereignty and jurisdiction in accordance with international law. With the resolve to protect its legal rights, Vietnam is ready to resolve disputes through peaceful methods," Hang said.

Vietnam wants concerned countries to contribute to the maintenance of peace and security at sea and in the air space in accordance with international law, she said.

Asked whether Vietnam would bring up the issue with the United Nations Security Council and possibly sue China, Hang reiterated that Vietnam "resolutely and persistently" protects its sovereignty and jurisdiction through peaceful methods in accordance with international law.

The issue of Chinese vessels infringing Vietnamese waters in the South China Sea had cast a shadow over the 52nd ASEAN Foreign Ministers' Meeting held in Bangkok, Thailand, between July 29 and August 3.

Vietnam’s Deputy Prime Minister and Minister of Foreign Affairs Pham Binh Minh had denounced China's activities at the ASEAN meeting, calling them illegal and serious violations of Vietnam's sovereignty and jurisdiction rights.

His counterparts from the U.S., Japan and Australia also expressed concerns at the meeting over aggression that intimidate oil and gas activities in the South China Sea.

The U.S. National Security Advisor John Bolton accused China of "bullying" in a tweet on Tuesday, saying China’s efforts to intimidate others out of developing resources in the South China Sea is disturbing.