US President Joe Biden and Chinese leader Xi Jinping began their first conversation since March on Thursday, a call the White House says is intended to keep relations stable despite rising tensions over Taiwan and the war in Ukraine.

The exchange is overshadowed by friction over a possible trip to Taiwan next month by House Speaker Nancy Pelosi, a prospect that has prompted warnings of a “firm and strong” response from China. US Ambassador to China Nicholas Burns said in June that relations with Beijing have deteriorated to probably “the lowest moment” since former President Richard Nixon’s landmark visit to China in 1972.

China views any Taiwan trip by Pelosi as a violation of the deal that helped establish ties between Washington and Beijing a half century ago, including an American promise to cease formal relations with Taipei.

Pelosi has refused to confirm her travel schedule, citing security concerns. The itinerary includes stops in Indonesia, Japan and Singapore, a person familiar with the matter said Wednesday, adding that Taiwan remains off the official itinerary.

The White House hasn’t taken a public position on any Taiwan visit, saying it’s Pelosi’s decision, but Defense Department officials have privately expressed unease to the speaker and her staff. The American, Chinese and Taiwanese military are all regularly active around the island and an aircraft carrier battle group led by the USS Ronald Reagan entered the South China Sea this week as part of what the Navy said was a scheduled operation.

Wang Yang, the Communist Party’s No. 4 official, told a meeting Tuesday that “no individual and no force should underestimate the resolve, the will and the ability of the Chinese people to defend their national sovereignty and territorial integrity.”

Biden, who had been isolating with Covid-19 until yesterday, has said little publicly about the matter. It isn’t clear whether he supports the trip or if he’s spoken about it with Pelosi directly. He told reporters last week that the US military didn’t think a Pelosi visit was a good idea, prompting consternation in Taiwan.

The president and his advisers also continue to assess whether to cut some of the tariffs imposed on Chinese imports by his predecessor, former President Donald Trump, though US officials have played down the likelihood of the topic coming up in the call.

“The key thing is that the president wants to make sure that the lines of communication with President Xi remain open because they need to,” John Kirby, a National Security Council spokesman said. “There’s issues where we can cooperate with China on and then there’s issues where obviously there’s friction and tension.”

Kirby added that Biden would “reaffirm that there’s no change to America’s commitment to the ‘One China’ policy, none, zero.”