Anti-China rallies in two main cities in Vietnam, amid rising tensions over Beijing’s claims to the South China Sea, were quickly dispersed Sunday by security forces as the protesters tried to approach the Chinese Embassy in Hanoi.

Approximately 20 people, among some 200 odd protesters, some waving banners and chanting "Down with China's aggression," were arrested after the half-hour rally, the AFP reported.

Security forces also broke up a similar anti-China demonstration attended by hundreds of people in  Ho Chi Minh City (formerly Saigon), the report said, citing eyewitnesses.

According to a BBC report, it is the first anti-China protest in Ho Chi Minh City in more than a year.

Few public protests are tolerated by the authoritarian regime, which gives greater importance to political and social stability.

The South China Sea has long been a bone of contention between China and several members of the Association of South East Asian Nations. China lays claim to almost the entire sea, including areas recognized by the U.N. as the exclusive economic zones of other neighbors, the Philippines, Vietnam, Taiwan, Malaysia and Brunei.

In July, the Vietnamese government had allowed a similar anti-China demonstration to go ahead in Hanoi, although security forces blocked the rally when it came within 300 feet of the Chinese Embassy.

Beijing’s relations with Hanoi has grown worse in the past weeks over China’s decision to include in its revised passports an offending map, which shows Beijing staking claim on almost the entire South China Sea.

China asked Vietnam last week to immediately stop its unilateral oil exploration in disputed areas and not harass Chinese fishing boats, days after Hanoi announced its plans to step up its maritime presence in the region.

Chinese Foreign Ministry spokesman Hong Lei made the comment Thursday in response to a Vietnamese Foreign Ministry spokesman's remarks the previous day that criticized China for violating its sovereignty and accused Chinese boats of sabotaging an exploration operation that was being carried by Vietnam’s state oil firm Petrovietnam, Xinhua news agency reported.

Hanoi has finalized its decision to deploy civilian-led patrols, supplemented by marine police and a border force, from Jan. 25, to stop foreign vessels that violate fishing laws within Vietnam's waters, Reuters reported, citing Vietnam's government and state media.

Chinese media had recently announced new government rules authorizing police in the southern province of Hainan to board and seize foreign ships in the South China Sea, Reuters reported.

Hong said last week that China and Vietnam were currently in negotiations over the waters.