BEIJING (Reuters) - China on Thursday demanded that Vietnam apologize to a Chinese tourist who says he was beaten up by Vietnamese border guards after failing to pay a bribe, an incident that provoked outrage among Chinese internet users.

The call comes a month after the neighbors pledged to safeguard peace in the disputed South China Sea, nearly all of which is claimed by China, although Vietnam and four other Asian nations also have claims in the oil-rich area.

Last week, a group of about eight uniformed men beat a Chinese man surnamed Xie in Vietnam’s northern city of Mong Cai on the border with China, after he failed to pay a “tip”, the state-run China News Service said on Saturday, citing Xie.

The head of the consular affairs office of China’s foreign ministry “had a special appointment” on Thursday with the Vietnam ambassador to “once more express our stern position,” Foreign Ministry spokesman Geng Shuang said.

“China demands that Vietnam apologize and pay compensation to the victim, severely handle those involved and take effective measures to ensure an incident does not happen again,” Geng told a regular news briefing.

Vietnam has already suspended eight people involved in the incident, he added.

On Wednesday, Vietnam’s Foreign Ministry told Reuters by email that it was “clarifying” information on the incident provided by China, and would “resolve the issue (according to) the nature of the event”.

Xie, accompanied by his mother and fiancee, was returning from a trip to Vietnam planned for the couple to take location photographs ahead of their wedding, the agency said.

The fiancée, identified as Xiao Li, told China News the women had tried to halt the beating and make a video recording of it, only to be restrained, and have their phones confiscated.

State media pictures of a bruised Xie in hospital were widely shared online, sparking angry comments calling the incident a matter of national pride for China and targeting Vietnam.

Chinese tourists made up nearly 30 percent of all visitors to Vietnam last year at just under 2.7 million, figures from Vietnam’s tourism administration show.

The border crossing between Mong Cai and the city of Dongxing in China’s southern region of Guangxi is the main crossing-point between the two nations.

Although China and Vietnam regularly talk up their common interests as “traditional” friends and neighbors in public statements, conflicting claims of sovereignty in the South China Sea have become a major source of tension in recent years.