About 100 anti-China protesters marched peacefully in Vietnam Sunday despite a heavy security clampdown and a vow by both countries to rein in public opinion over tensions in the South China Sea. Protests -- which are not common in authoritarian Vietnam -- have taken place in the capital Hanoi for five weekends in a row over the maritime dispute. Plainclothes and uniformed security agents poured into the area around the Chinese embassy and sealed off surrounding roads, but about 40 protesters penetrated the cordon to gather some distance from the embassy before marching towards central Hanoi, trailed by riot police and other security personnel. More people joined the march along the way, shouting that two South China Sea archipelagos, the Spratlys and Paracels, belong to Vietnam. The two countries have longstanding sovereignty disputes over the potentially oil-rich island groups, which also straddle commercial shipping lanes vital for global trade. Tensions flared and protests began after Hanoi in late May accused Chinese marine surveillance vessels of cutting the exploration cables of an oil survey ship inside its exclusive economic zone. In a second incident, Hanoi alleged a Chinese fishing boat rammed the cables of another ship in the 200-nautical-mile zone. Vietnam then held a live-fire naval drill off its central coast. \"China must respect Vietnam\'s exclusive economic zone,\" said a sign held aloft by the demonstrators. \"Anti-China,\" another said simply, in English. Analyst have said that Vietnamese authorities permitted the anti-China rallies, which have drawn up to about 300 people, because they served the government\'s purpose of expressing displeasure with Beijing over the dispute. Two protests had taken place in southern Ho Chi Minh City but there have been none there since June 11. A person involved in the rallies told AFP that security forces had \"intimidated\" people there. In Hanoi, some activists feel their demonstrations were \"in vain\" after China and Vietnam held talks on June 25 in Beijing, said the source who did not want to be identified. State media from both countries said the two sides agreed at the talks to resolve their maritime territorial disputes peacefully \"through negotiations and friendly consultations\". The official Vietnam News said \"they also laid stress on the need to steer public opinion in the correct direction.\" The apparent olive branch between the neighbours came as the United States and Philippines readied for joint naval exercises in the face of Chinese actions and after the US called for Beijing to help lower the temperature.