The United States on Friday warned China not to interfere in Taiwan's upcoming presidential elections, urging "responsible behavior on all sides."

The lead-up to the self-ruled island's 13 January poll is being closely watched — including by policymakers in Beijing and Washington — as it could determine the future of Taiwan's relations with an increasingly bellicose China. 

"Our strong expectation and hope is that those elections be free of intimidation, or coercion, or interference from all sides," said the US ambassador to China, Nicholas Burns.

Taiwan is a major tension point between China and the United States, Taipei's most important ally.

China claims self-ruled Taiwan as its own and has repeatedly vowed to seize it one day, by force if necessary.

"The United States is not involved and will not be involved in these elections," Burns said.

Taiwan is a major semiconductor producer, and the Taiwan Strait remains a crucial shipping route for global trade.

More broadly, Burns noted that "China wishes to become the strongest power in the Indo-Pacific," referring, for example, to its recent activities in the South China Sea.

The United States and China are "in a competitive relationship" when it comes to their militaries and economies, he said.

But Burns also noted the economic giants' ability to agree, particularly in the wake of a November meeting between the two countries' presidents, Joe Biden and Xi Jinping.

The two leaders agreed to restore military-to-military communications and tackle the fentanyl trade, a drug which causes tens of thousands of US overdose deaths each year. 

Burns additionally called to strengthen people-to-people relations between the two countries, noting that there were "15,000 American students six or seven years ago in China. Last year, we were down to 350."

Before the pandemic, there were 354 direct flights per week between the two countries, compared to only 70 at present.