Trump, speaking at the White House on Thursday during a joint news conference with Italian Prime Minister Paolo Gentiloni, cited “some very unusual moves” that the Chinese government had “made over the last two or three hours.”

Trump gave no clue what steps he was referring to, although the Nikkei Asian Review reported hours earlier that Beijing may cut crude oil to North Korea if it conducts another test of a nuclear warhead, citing Zhang Liangui, a professor at the Chinese Communist Party’s Central Party School

The U.S. president met earlier this month with Xi and urged him to do more to rein in North Korea’s nuclear weapons and missile programs. Trump said later that he was dialing back his hard-line approach to China on trade because he was convinced of the Chinese leader’s commitment to address the problem.

North Korean leader Kim Jong Un recently has accelerated missile and nuclear tests, heightening concerns over the regime’s efforts to develop a nuclear warhead capable of striking the U.S. The Trump administration has warned that it is considering a range of options to stop North Korea from developing the capability, including a preemptive military attack.

Vice President Mike Pence said Wednesday that while the U.S. is using economic and diplomatic approaches “the sword stands ready.” North Korea’s state-run newspaper on Thursday carried a threat by the regime to launch its own “super-mighty preemptive strike” that would devastate U.S. and South Korean forces on the peninsula.

The regime’s most recent ballistic missile launch, conducted last Sunday, failed.

North Korea may have between 10 and 25 nuclear weapons, analysts say, as well as active cyberwarfare capabilities, a biological weapons research program and one of the world’s largest chemical weapons stockpiles. The U.S. also must consider implications for its ally South Korea, whose capital of Seoul, with 10 million residents, sits 35 miles (56 kilometers) south of the border, within range of conventional artillery.

As Trump has sought to increase pressure on North Korea, the Pentagon ordered the USS Carl Vinson to head toward Korean waters. The aircraft carrier was headed that way after initial confusion about an itinerary that first had it bound for joint exercises with Australia.