US President Donald Trump’s close ally, Senator Steve Daines, will lead a bipartisan delegation to China next week, according to sources, even as Washington steps up pressure on Beijing over trade, technological competition, and its ties to Iran, ahead of a closely watched leaders’ summit on May 14-15.

According to people familiar who requested anonymity, the five-member delegation led by Daines, a Republican from Montana, will begin its visit on May 1, with stops in Shanghai and Beijing.

The...