SEOUL, South Korea — The United States and its allies will bolster sanctions and go on the defensive against North Korea in ways that China may not like if Beijing fails to lend greater support to efforts to curb the North’s nuclear ambitions, a top American diplomat said here on Wednesday.

The diplomat, Deputy Secretary of State Antony J. Blinken, made the warning a day before he planned to meet with Chinese officials in Beijing to pressure them to use their economic leverage over North Korea to force it to end its nuclear weapons program.

“I think what we will be talking to China about is that we will, both in terms of sanctions and in terms of our defense postures, have to take additional steps in order to use the leverage we have in order to defend ourselves and our allies if North Korea doesn’t change its behavior,” Mr. Blinken said in an interview.

Some of those steps “won’t be directed at China, but China probably won’t like them,” he said.

Mr. Blinken refused to go into detail. But he said that “everything is on the table,” including so-called secondary sanctions, of the type the United States most recently used against Iran, which would target third-party countries doing business with North Korea.