"As Vietnam looks at the issue, Chinese oil survey vessel Haiyang Dizhi 8 and its escorts have continued seriously violating Vietnam’s sovereignty and jurisdiction right in its exclusive economic zone and continental shelf," she said at a news briefing on Thursday.

She said Vietnam’s sovereignty and jurisdiction over the waters are recognized by the United Nations Convention on the Law of the Sea (UNCLOS) signed in 1982.

Vietnam has made its point about the negative impacts caused by the operation of these vessels to the relations of the two nations as well as the peace and stability in the East Sea.

"For all these reasons, Vietnam demands that China immediately stops this activity and remove the vessels," she said

Regarding recent statements by China on Vietnam’s economic activities in Vietnamese waters, she said the nation has consistently affirmed that all of its maritime economic activities, including oil and gas exploitation, are deployed within the exclusive economic zone (EEZ) and continental shelf that completely belongs to Vietnam, as defined by the UNCLOS, of which both Vietnam and China are members.

Hang emphasized that the UNCLOS was the only legal basis for nations to identify their waters. This has been followed by all nations and is recognized by both international courts and reputed international lawyers.

There is no nation that can make demands about waters in the East Sea that go beyond what has been regulated by the UNCLOS, she stressed again.

"Illegal, unsuitable claims against UNCLOS cannot be the basis for asserting that disputed or overlapping waters exist in the East Sea. Acts that hinder Vietnam's oil and gas activities in its waters are violations of international law and the UNCLOS," Hang said.

Chinese oil survey vessel Haiyang Dizhi 8 and escorts returned 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.

Hang’s latest statement is the third time Vietnam has raised its voice to demand that China withdraws the vessels after their return.

Vietnam had publicly condemned the vessels' return last month.

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 aggressive intimidation of legitimate oil and gas activities in the South China Sea.