More than a dozen demonstrators who gathered near the Chinese Embassy in Hanoi were herded onto buses by police when they tried to assemble for the sixth straight Sunday to express outrage over an ongoing spat with China involving disputed territory in the South China Sea.

Associated Press Television News assistant Hau Dinh was filming the protest when he was also forced onto a bus with armed police. Two other Vietnamese journalists — a cameraman from Japanese public broadcaster NHK and a news assistant from Japanese newspaper Asahi Shimbun — were also detained, police said.

Dinh, the other journalists and the protesters — including a mother and her 5-year-old son — were released after being held and questioned for about three hours.

Demonstrations are rare in Vietnam, where the Communist government maintains tight controls, but Hanoi has permitted groups of up to about 200 protesters to gather for the past five weeks and march through the streets shouting anti-China messages. Journalists have been allowed to photograph and film the rallies despite a heavy security presence.

But officials from Vietnam and China met in Beijing two weeks ago and issued a joint statement saying they had agreed to negotiate to peacefully resolve the issue.

Vietnam claims Chinese boats hindered oil exploration activities within its exclusive economic zone, 200 nautical miles off the coast. China accuses Vietnam of endangering Chinese fishermen in a contested area near the resource-rich Spratly Islands, which are claimed in all or in part by both countries and several other Asian nations.