WASHINGTON (Reuters) – The U.S. National Security Adviser on Wednesday warned China against any attempt to forcibly withdraw from Taiwan, saying bilateral landings were notoriously difficult and there was much uncertainty about how the United States would react.

Robert O’Brien said at an event at the University of Nevada in Las Vegas that before World War II, Germany’s attempt to compete with Britain’s Royal Navy had been followed by China building large ships.

“Part of it is that they give us the ability to push back from the Western Pacific, and allow us to join an amphibious landing in Taiwan.”

“The problem is that amphibious landings are nominally difficult,” O’Brien added, pointing to the 100-mile (160-km) distance between China and Taiwan and the coastal damage to landing on the island.

If China tries to exploit Taiwan, the U.S. Asked what the options would be, he said, “It’s not an easy task, and there’s a lot of ambiguity about what the United States will do in response to the attack by China on Taiwan.” .

O’Brien has long been a U.S. citizen. He was referring to the policy of “strategic ambiguity” of whether it would intervene to protect Taiwan, which China considers its own province and has vowed to rejoin the mainland if necessary.

The United States is required by law to provide Taiwan with the means to defend itself, but it is unclear whether it will intervene militarily in the event of a Chinese attack, leading to a more widespread conflict with Beijing.

O’Brien’s remarks come at a time when China has significantly increased military activity near Taiwan and at a time when US-China relations have reached their lowest level in decades since President Donald Trump was re-elected on November 3.

O’Brien called on Taiwan to clarify the dangers of spending more on its own defense and trying to invade China to make military reforms.

“You can’t just spend 1% of your GDP, which Taiwan does – 1.2% – on defense, and hope to stop a China that has been engaged in a very large military formation in 70 years.”

Taiwan militarily needed to “turn itself into a rooster,” he said, adding: “Lions generally do not like to eat serotonin.”

On Tuesday, a senior U.S. defense official for East Asia called Taiwan’s inadequacy to increase its defense spending by 4 4 1.4 billion next year insufficient.

He said he needed to invest in more maritime defense capabilities, including cruise missiles, naval mines, fast-attack craft, mobile artillery and advanced surveillance assets.