President Joe Biden said the Pentagon did not support a planned visit to Taiwan by Nancy Pelosi, following reports that the Speaker of the House of Representatives was set to become the most senior US politician to visit the country in 25 years.

The Financial Times reported this week that Pelosi intends to travel to Taiwan in August, following a cancelled trip in April when the 82-year-old Democrat caught Covid-19. Asked if he believed it was a good idea for the Speaker to visit Taiwan, Biden said the US defence department was opposed.

“The military thinks it’s not a good idea right now,” he told reporters on Wednesday evening.

The White House did not respond to a question about who in the military — defence secretary Lloyd Austin or General Mark Milley, chairman of the joint chiefs — held that view.

One person familiar with the situation said the military provided several briefings on the topic. “Traditionally, the military only lays out risks and costs associated,” he said.

The FT this week reported that Pelosi would lead a delegation of lawmakers to Taiwan, Japan, Singapore, Indonesia and Malaysia. The group is also expected to visit US Indo-Pacific Command in Hawaii.

On Thursday, Pelosi told reporters: “I think that it’s important for us to show support for Taiwan.”

China this week said it would respond with “strong measures” if Pelosi went ahead with the visit to Taiwan, a democratically ruled country over which Beijing claims sovereignty. The last Speaker to visit Taiwan was Newt Gingrich, the Republican lawmaker. The US House Speaker is the second in the order of presidential succession, giving a visit particular prominence.

The visit would come at a very sensitive time for China. Pelosi was planning to visit after the August 1 anniversary of the founding of the People’s Liberation Army and months before the Communist party holds its 20th Congress, when President Xi Jinping is expected to claim an unprecedented third term as leader.

Mike Gallagher, an influential Republican lawmaker on China policy, called for Pelosi to proceed with the trip.

“This is a bad message from the president and an overall weak message for US foreign policy,” he said. “I urge Speaker Pelosi not to back down.”

The debate over whether Pelosi should visit Taiwan comes amid rising concern about assertive Chinese military activity around the island and anxiety about the possibility that Beijing could take military action.

Since Russia’s invasion of Ukraine, multinational companies have been asking for security briefings about the probability of the US and China going to war.

Underscoring those concerns, Biden said recently in Tokyo that the US would intervene militarily to defend Taiwan if it came under attack. Biden and Xi will almost certainly discuss Taiwan when they speak in the coming weeks.

The US president said he expected to have a call with his Chinese counterpart within 10 days. In their last virtual meeting, Biden told Xi that it was important that they did not allow the intensifying competition between the global powers to “veer into conflict”.

At the Aspen Security Forum on Wednesday, CIA director Bill Burns said he “wouldn’t underestimate President Xi’s determination to assert Chinese control . . . over Taiwan” and added that the risks of military action “become higher . . . the further into this decade that you get”.

Speaking about the effect that Russia’s invasion of Ukraine would have on China’s calculation about Taiwan, he said Beijing was taking lessons from Moscow’s actions.

“Our sense is that it probably affects less the question of whether the Chinese leadership might choose some years down the road to use force to control Taiwan, but how and when they would do it,” said Burns.

“If there’s one lesson I think they may be drawing from [Russian president Vladimir] Putin’s experience in Ukraine, [it] is you don’t achieve quick, decisive victories with underwhelming force . . . I suspect the lesson the Chinese leadership and military are drawing is that you’ve got to amass overwhelming force.”

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