North Korea has carried out another test of a rocket engine that the United States believes could be part of its program to develop an intercontinental ballistic missile, a U.S. official told Reuters on Thursday.

The United States assessed that the test, the latest in a series of engine and missile tests this year, could be for the smallest stage of an ICBM rocket engine, the official said, speaking on condition of anonymity.

A second U.S. official also confirmed the test but did not provide additional details on the type of rocket component that was being tested or whether it fit into the ICBM program.

One official said he believed the test had taken place within the past 24 hours.

The disclosure of the engine test came a day after the United States pressed China to exert more economic and diplomatic pressure on North Korea to help rein in its nuclear and missile programs during a round of high-level talks in Washington.

U.S. President Donald Trump has warned that a “major, major conflict” with North Korea is possible over its weapons programs, although U.S. officials say tougher sanctions, not military force, are the preferred option.

China’s top diplomat, Yang Jiechi, told Trump in a meeting at the White House that Beijing was willing to “maintain communication and coordination” with the United States in an effort to diffuse tension on the Korean peninsula, according to a statement from China’s Foreign Ministry on Friday.

The head of the U.S. Defense Intelligence Agency told Congress last month that North Korea, if left unchecked, was on an “inevitable” path to obtaining a nuclear-armed missile capable of striking the U.S. mainland.

Still, experts say Pyongyang could still be years away from have a reliable ICBM capability.

The continental United States is around 5,600 miles (9,000 km) from North Korea. ICBMs have a minimum range of about 3,400 miles (5,500 km), but some are designed to travel 6,200 miles (10,000 km) or farther.

Any military solution to the North Korea crisis would be “tragic on an unbelievable scale”, Trump’s defense secretary, Jim Mattis, said last month.

The United States, meanwhile, is ramping up capabilities to defend against the threat from North Korea, staging its first-ever successful test to intercept an incoming ICBM-type missile in May.

But a test on June 21 of a new capability being developed by the United States and Japan to defend against shorter-range missiles failed to hit its target, the U.S. Missile Defense Agency said on Thursday.

It was the second such test of the SM-3 Block IIA interceptor, which is being developed by Raytheon. The previous intercept test, conducted in February, had been successful.