MANILA - President Rodrigo Duterte said early Saturday he assured Chinese President Xi Jinping that American troops would never set foot on Pag-asa Island in the disputed South China Sea as he asked why China's ships were surrounding the area.

Recalling "the last time" he met with the Chinese leader, Duterte said he was aware of repercussions if US presence would be allowed on the island.

The Philippines and the US have a standing defense treaty under which Americans would defend the country in case of external aggression.

"I was not angry, pero sinabi ko (but I said), 'Did I not tell you Mr. President that I will never allow the Americans to set foot on any of the islands controlled by the Philippines, that we will not start any war, and that I will never allow American weapons to be stationed in that island?'" he said during a television interview over Sonshine Media Network.

Duterte did not mention a specific date of their meeting but he was known to have last met with Xi in April, when he went to Beijing for the Belt and Road Forum.

"So why are you surrounding my island with so many ships? You're wasting your gasoline... might as well give it to us," he added.

The island under Palawan is in the West Philippine Sea, the country's exclusive economic zone (EEZ) in the disputed waters where the Philippines has long maintained a military detachment. It is also home to a civilian community.

The President said the presence of US soldiers on the Philippine-occupied island could have serious diplomatic implications. The US has been watchful of the situation in the South China Sea, pressing for freedom of navigation in the vital waterway.

Citing his statement to Xi, Duterte said: "I told you, 'I will not allow, as long as I am President, any American to set foot on that Pag-asa Island because I know it will create really trouble.'"

It was the first time Duterte spoke in detail about the bilateral meeting with the Chinese leader. Malacañang had said in the aftermath of the meet that both sides agreed that "the situation can be managed by the mechanism of bilateral negotiations but it should not affect the cooperation" between the two countries.

• Duterte raises PH concerns over South China Sea incursions with China's Xi

Weeks before the April meeting between the two leaders, reports surfaced about the presence of hundreds of Chinese ships around Pag-asa Island.

• Hundreds of Chinese vessels circling Pag-asa Island: military

In his latest remarks, Duterte did not reveal Xi's explanation on why several Chinese ships continued to patrol waters deemed part of the Philippines.

The President did not also say if he confronted Xi over China's illegal mass harvesting of giant clams in the disputed waters.

"Okay na siguro kasi wala na namang reklamo ang mga fishermen," Duterte said.

(It think it's okay now because the fishermen are no longer complaining.)

• 'Filipino scientists seeded giant clams, Chinese fishermen stole them'

The Philippines and China have seen improved ties under the Duterte administration as he has shelved the country's landmark July 2016 victory before a United Nations-backed tribunal that invalidated Beijing's sweeping claims in the South China Sea.

China has ignored the ruling and ramped up its militarization efforts in the area.

Aside from the Philippines, Malaysia, Brunei, Vietnam and Taiwan have partial claims to the resource-rich waterway and its myriad shoals, reefs and islands.

The United States, while not a party to the maritime dispute, has been calling for restraint and freedom of navigation on the South China Sea.