BEIJING — China and two of its neighbors, Vietnam and India, were locked in a new dispute on Tuesday over energy exploration in the South China Sea, a signal that Beijing plans to continue its hard line in the increasingly contentious waterway.

Vietnam accused a Chinese fishing boat of cutting a seismic cable attached to one of its vessels exploring for oil and gas near the Gulf of Tonkin, an act apparently intended to inhibit Vietnam from pursuing energy deposits.

Vietnam said Tuesday that in retaliation, it would send out new patrols, which would include the marine police, to guard against increasing encroachment by Chinese fishing boats in the South China Sea. India, which operates several joint ventures with Vietnam’s national energy company, Petro Vietnam, said it would consider sending navy vessels to protect its interests in the South China Sea.

The latest episode followed an announcement by Hainan Province in southern China last week that Chinese vessels would board and search ships in contested areas of the waterway, which includes vital shipping lanes through which more than a third of global trade moves.