A Chinese fighter jet flew perilously close to a US military aircraft this week in a "very dangerous" incident in international air space east of Hainan Island, the Pentagon said Friday.

The episode raised tensions and underlined the growing rivalry between the United States and China, with Beijing building up its military and asserting its territorial claims across the Pacific.

"On August 19, an armed Chinese fighter jet conducted a dangerous intercept of a US Navy P-8 Poseidon patrol aircraft that was on a routine mission," spokesman Rear Admiral John Kirby told a news conference.

The close call occurred about 135 miles (220 kilometers) east of China's Hainan, he said.

"We have registered our strong concerns to the Chinese about the unsafe and unprofessional intercept, which posed a risk to the safety and the well-being of the air crew and was inconsistent with customary international law," Kirby added.

The move also threatened to jeopardize longstanding US efforts to bolster relations with China's military, he said, at a time when officials have touted progress in forging a dialogue with Beijing's top brass.

The armed Chinese warplane came close to the surveillance aircraft three times, flying underneath the American plane, at the P-8's nose and then in parallel with the wingtips, less than 30 feet (nine meters) apart, according to Kirby.

In approaching the P-8, the Chinese jet at one point performed a barrel roll, apparently to display its weapons.

"The Chinese jet also passed the nose of the P-8 at 90 degrees with its belly toward the P-8 Poseidon, we believe to make a point of showing its weapons load," Kirby said.

The intercept was "very, very close, very dangerous."

The skies over Hainan Island were the scene of a major international incident in April 2001, when a Chinese fighter jet collided with a US Navy EP-3 spy plane.

The collision left one Chinese pilot dead and forced the American plane to make an emergency landing on Hainan. Chinese authorities initially detained the 24-member American crew for more than a week until both governments worked out a face-saving deal for their release.

Washington and Beijing have long disagreed over aviation and maritime rights in the strategic South China Sea, with the Americans insisting the area is part of international waters and airspace.

But China argues it is part of the country's "exclusive economic zone."

US naval ships in the area have had some tense encounters with Chinese vessels in recent years, with the Pentagon alleging their warships had to take emergency evasive action to avoid collisions at sea.

Last week, China accused the United States of fueling tensions in the South China Sea and has rejected a US proposal for a multilateral deal that would seek to freeze provocative actions in the region.

Beijing claims the area almost in its entirety and is at locked in territorial disputes with the Philippines, Vietnam and other neighboring states.