Plans for Nancy Pelosi, the US House speaker, to visit Taiwan have prompted opposition from China and the American military but support from Republicans in Washington, including former members of the Trump administration.

Trump’s second secretary of defense, Mark Esper, told CNN: “I think if the speaker wants to go, she should go.”

Mike Pompeo, Trump’s second secretary of state, tweeted: “Nancy, I’ll go with you. I’m banned in China, but not freedom-loving Taiwan. See you there!”

No date has been set for a Pelosi visit to Taiwan, a self-governing democracy that Beijing claims is a breakaway province. Many observers expect some form of military action by China some time soon, particularly in light of the Russian invasion of Ukraine.

China has said a Pelosi visit would “severely undermine” its “sovereignty and territorial integrity, gravely impact the foundation of China-US relations, and send a seriously wrong signal to Taiwan independence forces”.

Joe Biden said last week: “I think that the military thinks it’s not a good idea right now. But I don’t know what the status of it is.”

The White House has not weighed in officially. On Monday, Biden’s press secretary, Karin Jean-Pierre, said: “The administration routinely provides members of Congress with information and context for potential travel, including geopolitical and security considerations.

“Members of Congress will make their own decisions.”

The state department spokesperson, Ned Price, said: “I will just restate our policy, and that is that we remain committed to maintaining cross-strait peace and stability and our ‘One China’ policy” – a reference to the US position that recognises Beijing as the government of China but allows for informal relations and defense ties with Taiwan.

That was a policy Trump initially seemed to jeopardise, telling Fox News in December 2016, after he won the election: “I don’t know why we have to be bound by a ‘One China’ policy unless we make a deal with China having to do with other things, including trade.”

In office, Trump agreed to follow the policy. But his administration was vociferous in its support of Taiwan and antagonism toward Beijing, with some observers suggesting officials wanted to force the Biden administration, which followed Trump’s, into confrontation with China.

Pelosi has said it is “important for us to show support for Taiwan”. She also said she believed that when Biden referred to US military concerns, he meant “maybe the military was afraid our plane would get shot down or something like that by the Chinese”.

Senator Ben Sasse, a Republican from Nebraska, said: “Speaker Pelosi should go to Taiwan, and President Biden should make it abundantly clear to Chairman Xi [Jinping] that there’s not a damn thing the Chinese Communist party can do about it.

“No more feebleness and self-deterrence. This is very simple: Taiwan is an ally and the speaker of the House of Representatives should meet with the Taiwanese men and women who stare down the threat of Communist China.”

Also on Monday, the New York Times reported that the Biden administration “has grown increasingly anxious … about China’s statements and actions regarding Taiwan, with some officials fearing that Chinese leaders might try to move against [it] … over the next year and a half – perhaps by trying to cut off access to all or part of the Taiwan Strait, through which US naval ships regularly pass”.

The Democratic senator Chris Coons of Delaware, who is close to Biden, told the Times: “One school of thought is that the lesson is ‘go early and go strong’ before there is time to strengthen Taiwan’s defenses. And we may be heading to an earlier confrontation – more a squeeze than an invasion – than we thought.”

The Times also said the White House was “quietly work[ing] to try to dissuade” Pelosi staging the first visit by a speaker to Taiwan since 1997.

The Republican speaker who made that trip, Newt Gingrich, said: “What is the Pentagon thinking when it publicly warns against Speaker Pelosi going to Taiwan?

“Timidity is dangerous.”