For the second consecutive weekend, Vietnamese authorities clamped down on anti-China protests as they came under increasing pressure to take strong action against Beijing over territorial claims in the South China Sea.
Around two dozen demonstrators marching near the Chinese embassy in Hanoi on Sunday were rounded up, herded into buses, and driven away. Some of them were later detained.
About 50 people, including a group of intellectuals, joined the protests which were quickly dispersed after the arrests.
Citizen journalist photos of the protests showed one man being kicked on the ground by police.
International watchdog Human Rights Watch condemned the crackdown.
"The Vietnamese authorities' defiance of their international human rights commitments is on full display with this latest wave of arrests and violence against peaceful demonstrators raising concerns about China," said Phil Robertson, Deputy Director of Human Rights Watch's Asia division.
The protesters shouted anti-China slogans and expressed anger over what they see as Chinese aggression in disputed territories in the South China Sea.
The rally, held for the seventh weekend in a row, was the latest in a series of protests sparked by confrontations between Chinese and Vietnamese vessels off the Spratly (in Chinese, Nansha) and Paracel (in Chinese, Changsha) Islands in June.
Public demonstrations are rare in Vietnam and usually restricted by the government, but authorities had allowed the protests to continue until last Sunday, when police detained a dozen protesters and journalists at the rally.
Anger at this weekend's protest also stemmed from recent Vietnamese charges that Chinese navy sailors last week had beaten up a Vietnamese fishing boat captain near the disputed Paracel Islands.
Coast guard officials said the incident, in which the Chinese navy confiscated the trawler's catch and forced it away from the area, occurred July 5, and was not reported until the fishermen returned last week.
Demonstrators at the protest on Sunday carried banners with slogans such as "China! Stop massacring innocent fishermen!" and "China's military expansion threatens world peace and security," in English, Chinese, and Vietnamese.
As local anger swelled over the Chinese actions, a group of 20 Vietnamese academics and former senior officials sent a petition to the Vietnamese leadership, calling for a stronger stance against China in the territorial dispute and greater freedom to hold anti-Beijing protests.
The petition, titled "On the Defense and Development of the Country in the Current Situation," was sent to the National Assembly, the country's parliament, and the politburo of Vietnam's Communist Party.
The document also addressed the broader issue of Chinese influence in Vietnam.
The list of 20 signatories included prominent academics, lawyers, and Vietnam's former ambassadors to China and Thailand.
Vietnamese academics in recent years have also submitted petitions to the authorities on issues such as on bauxite mining and the arrest of prominent dissidents.
But the driving force behind the anti-China protest is broader than this group of intellectuals and has been fueled by social media networks, including bloggers.
"You have Vietnamese from all groups of society—students, youths, intellectuals, and so forth—expressing their concerns over actions by China in what are Vietnamese waters," said Dan Hoang, spokesman for the U.S.-based Vietnamese pro-democracy party Viet Tan, which is banned in Vietnam.
"It reflects a longstanding attitude of the Vietnamese authorities that civil society groups have no role in debating or participating in national policies," he said in an interview.
"What we're seeing now is Vietnamese society asserting itself, wanting to be heard on an issue of crucial national importance," he said.
On Friday, Vietnam and the United States began a week of joint naval exercises despite objections from China.
Aside from Vietnam and China, the Philippines, Brunei, Malaysia, and Taiwan have overlapping claims to parts of the South China Sea, believed to be rich in oil and gas reserves and home to shipping lanes vital to global trade.
The disputes over territorial claims are expected to be discussed at the upcoming Association of Southeast Asian Nations (ASEAN) regional meeting later this month.
ASEAN Secretary-General Surin Pitsuwan said Thursday that the meetings "will provide the forum where issues on the South China Sea can be discussed openly and candidly."
Reported by Rachel Vandenbrink.