WASHINGTON (Reuters) – The U.S. Navy’s top officer asked his Chinese counterpart to exert influence on North Korea to help rein in its advancing nuclear and missile programs, a U.S. official said on Thursday.

Chief of U.S. Naval Operations Admiral John Richardson spoke with his Chinese counterpart Vice Admiral Shen Jinlong via a video teleconference.

“Richardson voiced his concern about the nuclear and missile programs and emphasized that China should use its unique influence over North Korea,” said the official, speaking on condition of anonymity.

The call lasted for an hour and the two talked about the need to “work together to address the provocative and unacceptable military behavior by North Korea,” the U.S. Navy said in a statement.

Last month U.S. President Donald Trump said Chinese efforts to persuade North Korea had failed.

Trump has hoped for greater help from China to exert influence over North Korea, leaning heavily on Chinese President Xi Jinping. The two leaders had a high-profile summit in Florida in April and Trump has frequently praised Xi while resisting criticism of Chinese trade practices.

North Korea recently said it conducted its first test of an intercontinental ballistic missile, and that it had mastered the technology to mount a nuclear warhead on the missile.

The United States has remained technically at war with North Korea since the 1950-53 Korean War ended in an armistice rather than a peace treaty. The past six decades have been punctuated by periodic rises in antagonism as well as rhetoric that has stopped short of a resumption of active hostilities.

Tensions rose sharply after North Korea conducted two nuclear weapons tests last year and carried out a steady stream of ballistic missile tests.

(Reporting by Idrees Ali; Editing by Jeffrey Benkoe)