Vietnamese demonstrators have rallied in Hanoi for a third straight Sunday to protest Chinese maritime practices, in an escalating regional dispute over potentially energy-rich islets in the South China Sea.

The protesters gathered at the Chinese embassy and marched through nearby streets demanding that Beijing stay out of what Hanoi insists is Vietnamese territory.

The demonstrations — a rare occurrence in Vietnam — stem from the biggest flare-up in bilateral tensions in decades. Neither side has demonstrated much willingness in recent weeks to back down from the competing claims to the Spratly island chain or other maritime territories.

Last week, China dispatched one of its largest naval patrol vessels to Singapore, on a circuitous voyage near disputed territories claimed by Vietnam and the Philippines. Beijing said the excursion was aimed at promoting maritime cooperation with the city-state.

China also said it will expand its South China Sea naval force over the next decade, in a move analysts say is aimed at asserting Chinese sovereignty over large swaths of disputed territory.

Last month, Vietnam complained that a Chinese patrol ship severed an exploration cable trailing from an oil survey ship operating in waters inside Vietnam's exclusive economic zone. The Philippines also has complained of Chinese patrol boats interfering with oil exploration off its western coast.

In each case, China insisted its ships were operating appropriately in waters under Beijing's administration.

Some analysts have pointed out that countries other than China have long used visits to foreign ports as a way to improve diplomatic relations with other countries.

The U.S. aircraft carrier George Washington last year hosted leading Vietnamese political and military personnel during a visit to the Southeast Asian country.