China said Monday it would impose sanctions on Lockheed Martin and a defense division of Boeing that are part of a new sale of missiles to Taiwan worth nearly $2 billion.

"It is not the first time that Beijing has threatened sanctions upon US companies," said R. Clarke Cooper, the top State Department official in charge of arms sales.

"There have been threats and there have been provocations about that," he told a small group of reporters when asked about Chinese sanctions.

The United States is obligated under domestic law to provide weapons for self-defense to Taiwan, a self-ruling democracy that is claimed by Beijing.

China in recent months has entered Taiwan's air defense zone with growing frequency, while propaganda films have shown simulated attacks.

"Taiwan's security is central to stability in the Indo-Pacific region," Cooper said, adding that China has long understood that the United States will keep selling arms to Taiwan.

"The provocations that are coming from Beijing -- the bullying behavior, as one may assess -- that is where the provocateurs lie, not with Taiwan maintaining its own self-defense," he said.

"If anything, we are making sure that Taiwan is not bullied or overcome by Beijing."

The United States only recognizes Beijing, which considers Taiwan -- where China's defeated nationalists fled in 1949 -- to be a territory awaiting reunification.

But President Donald Trump's administration has been increasingly vocal in its support of Taiwan, including through two recent visits by senior officials.

Joe Biden, Trump's rival in Tuesday's election, also recently pledged in an op-ed in World Journal, a newspaper aimed at Chinese-Americans, to "deepen" ties with Taiwan.

Biden called Taiwan a "leading democracy, major economy, technology powerhouse," and hailed the island's exceptional success in keeping out Covid-19.