The commander of the U.S. Navy's Pacific Fleet said Monday that the time frame of China's possible attempt to take Taiwan by force was unpredictable, with Beijing apparently learning from the Russian invasion of Ukraine.

Adm. Samuel Paparo also called for the importance of "constant vigilance," in what appears to be remarks intended to play down an assessment voiced last year by the former Indo-Pacific Command chief Philip Davidson that China could invade Taiwan within "the next six years."

"I think the window of a potential unification by force is highly, highly unpredictable," Paparo told a group of reporters in Washington, while noting that the so-called Davidson window is "actually based on open source speeches" made by Chinese leaders.