Vietnam's President To Lam is urging China to follow the rule of law at sea. State media say he sat down on Tuesday with Xiong Bo, Beijing's ambassador in Hanoi.

Lam reportedly said he prioritizes friendly ties with China, and spoke highly about a series of deals made when President Xi Jinping visited Vietnam last year.

But Lam also made a point of mentioning the South China Sea, where the two countries have a long-running territorial dispute.

He reportedly called for a solution based on the 1982 United Nations Convention on the Law of the Sea.

Vietnamese authorities said earlier this month a Chinese Navy vessel was found conducting an illegal survey in their country's exclusive economic zone.

A foreign ministry spokesperson expressed deep concern to Beijing.