Associated Press

HANOI, Vietnam (AP) _ Vietnamese police broke up anti-China protests in two cities on Sunday and detained 20 people in the first such demonstrations since tensions between the communist neighbors flared anew over rival claims to the oil and gas-rich South China Sea.

Any sign of popular anger in tightly controlled Vietnam causes unease among the leadership, but anti-Chinese sentiment is especially sensitive. The country has long-standing ideological and economic ties with its giant neighbor, but many of those criticizing China are also the ones calling for political, religious and social freedoms at home.

Police initially allowed about 200 protesters to march from Hanoi’s iconic Opera House through the streets, but after 30 minutes ordered them to disperse. When some continued, they pushed about 20 of them into a large bus which then drove quickly from the scene. It was unclear where they were taken, but in the past people detained at anti-China protests have been briefly held and released.

As foreign tourists and Sunday morning strollers looked on, protesters shouted “Down with China” and carried banners bearing the slogan “China’s military expansion threatens world peace and security.”

Using loudspeakers, authorities urged them to disperse and tried to reassure them.

“The Communist Party and government are resolutely determined to defend our country’s sovereignty and territory through peaceful means based on international law,” it said. “Your gathering causes disorder and affects the party’s and government’s foreign policy.”

A smaller protest also took place in Ho Chi Minh city, according to blogger and activist Huynh Ngoc Chenh.

He said he was ordered to leave by police, but about 100 people gathered for 10 minutes before being dispersed.

“I’m frustrated,” he said by telephone. “There’s nothing to ban, the government should allow people to express their patriotism peacefully.”

Vietnam and China have long sparred over who owns the South China Sea, a dispute that the Philippines, Malaysia, Brunei and Taiwan are also parties to. Over the last two years, America’s diplomatic tilt to Southeast Asia and energy-hungry China’s growing assertiveness has focused international attention on the issue.

Vietnam last week alleged that Chinese shipping vessels sabotaged one of its seismic survey vessels in the South China Sea. This week the government warned Beijing not to do that again and presented a list of its violations in the disputed sea. China recently issued new passports containing a map showing the sea as belonging to it, causing anger in Hanoi and other regional states.

In the summer of 2011, there were two months of weekly protests in Hanoi, an unprecedented show of popular anger in the country. Earlier this year, there were also some demonstrations. Police dispersed them, gradually using more force as it become clear they were becoming a source of domestic opposition to the party.