“And as for China, they said ‘just come over and sign and everything will be delivered’.”

His comments were the latest in a near-daily barrage of hostility toward the United States that has raised questions about the long-standing alliance that is important to the US strategy of rebalancing its forces toward Asia and countering an assertive China.

US officials have downplayed Duterte’s remarks, focusing instead on the decades-long alliance which they have sought to bolster in recent years in response to China’s moves to enforce its claims over the South China Sea.

The White House said on Tuesday the United States had not received any formal communications from Duterte’s government about changing the relationship.

The United States is the single largest provider of arms to the Philippines, according to figures maintained by the Stockholm International Peace Research Institute (SIPRI), which tracks military expenditures globally.

The two countries have become more intertwined militarily in the last two years, holding more exercises and training, and making more US ship and aircraft visits under President Barack Obama’s shift of US military forces and diplomatic efforts toward Asia in the face of China’s rise.

The Philippines is the largest recipient of US funds in the Asia-Pacific region under the Foreign Military Financing programme, which is provided by the United States to help countries purchase American-made weapons and equipment. It received US$50 million under FMF in the 2015 fiscal year.

That dependence on US weapons and systems means the Philippine military would have to retool its command-and-control structure if it wanted to switch to Chinese or Russian systems, said Richard Javad Heydarian, a professor at De La Salle University in Manila and a former adviser to the Philippines House of Representatives.

“There will be some problems with configuration,” Heydarian said. “It takes years for the Philippines’ army to reorient itself with new technology.”

The Philippines spent US$3.9 billion on its military in 2015, according to SIPRI data. That spending has risen nearly every year since 2010, when it stood at US$2.4 billion, the data show.

Though Russia in particular could offer high-quality weapons systems, the Philippines would have to take into account their interoperability with existing American stock, said Lyle Goldstein, an expert on Chinese maritime issues at the US Naval War College.

“You can’t just buy a radar from this country and a missile from that country,” Goldstein said. “The weaponry has to work together.”

He noted that many Philippine officers were educated in the United States, linking the countries’ military cultures closely.

Russia and China do not have the same reputation of providing comprehensive training and support, said Amy Searight, until earlier this year the US deputy assistant secretary of defence for South and Southeast Asia.

“The United States is well known for being quite good at that full spectrum of support to build capabilities,” said Searight, now with the Centre for Strategic and International Studies in Washington. “It’s not just the weapons or the armaments or vehicles or equipment. It’s using those to build real capabilities.”

Most likely, Duterte’s aim is to signal to China that he is willing to tinker with existing US-Philippines military cooperation, even if on the margins, Heydarian said.

That might mean relocating the annual US-Philippines “Balikatan” military exercises away from the South China Sea, or refusing to further expand American military access to Philippine bases, he said.

Duterte could also be trying to strengthen his position in order to get better prices on military equipment from the United States, experts said. Russian and Chinese weapons are typically cheaper than American systems.