China sent the Trump administration "positive signals"  that it will increase economic sanctions to pressure ally North Korea to abandon its development of nuclear weapons and missiles, a threat that has raised the prospect of a military confrontation with the United States, the State Department revealed Monday.

“We’ve got a lot of positive signals from the Chinese but it takes time,” Susan Thornton, acting assistant secretary for East Asian and Pacific affairs, said on a conference call with reporters. “You don’t know if economic pressure works until it works.”

U.S. diplomats will meet with the Chinese and American allies at the United Nations later this month to discuss the way forward, Thornton said. But if the Chinese are unsuccessful, the U.S. will move to increase pressure on North Korea on its own.

“We’re going to be watching what the Chinese do,” she said. “We’re going to work with China and see if they do more. And if they do not cooperate or work with us we’ll change tacks and try to do more on our own.”

China is considered key to changing North Korea's behavior because it is an economic lifeline for its much smaller neighbor. But China has been reluctant in the past to use its leverage because its fellow communist country serves as a buffer between Chinese territory and U.S. troops stationed in South Korea. The Beijing government also worries about a flood of refugees crossing into China if it allowed the isolated nation's economy to collapse.

Thornton said the U.S. is not interested in a pre-emptive strike or regime change in North Korea, which is ruled by totalitarian leader Kim Jong Un, but that it is looking for some kind of signal from the mercurial Kim that his government is willing to stick to its international commitments to abandon its current path of developing and testing nuclear weapons and ballistic missiles that could reach the United States.

A missile test on Sunday resulted in an explosion almost immediately after liftoff. The test came as a U.S. aircraft carrier sailed in waters off the Korean peninsula, and hours before the Vice President Pence arrived in South Korea.

Pence warned North Korea on Monday that the "era of strategic patience is over" and that all options are on the table if Kim continues to threaten the region with his missile and nuclear testing programs. Speaking at the Demilitarized Zone that separates North and South Korea, Pence cited U.S. military strikes in Syria and Afghanistan this month as proof of President Trump’s willingness to use force, if necessary.

"North Korea will do well not to test his resolve or the strength of the armed forces of the United States in this region," Pence said.

North Korea has conducted five nuclear tests since 2006, the last in September. It also has conducted numerous medium- and long-range missile tests since Kim took power in 2011.

“We need to see some kind of demonstrable change in North Korean behavior,” Thornton said. “Such signals would not include things like launching illegal missiles like what happened over the weekend,” she added.