The US Department of Defense says it is monitoring events closely as China launched three days of military exercises around Taiwan on Saturday.

A Pentagon spokesperson said in a statement that Taiwanese President Tsai Ing-wen's recent US transit was "consistent with longstanding US policy."

The statement says there is no reason for Beijing to turn the transit into "something it is not or use it as pretext to overreact."

It adds that the US military will continue to "safely and responsively fly, sail and operate wherever international law allows."