WASHINGTON--U.S. Defense Secretary Mark Esper on Thursday said the United States still sees a political agreement on denuclearization as the best path forward on North Korea, but that American forces remained prepared to fight if necessary.

"We would urge restraint by Kim Jong Un," Esper said in an interview on Fox News.

North Korean leader Kim Jong Un said this week that there were no longer grounds for Pyongyang to be bound by a self-declared moratorium on intercontinental ballistic missile and nuclear bomb testing and that a "new strategic weapon" would be introduced in the near future.

A U.S. official, speaking on condition of anonymity, said there were no indications that North Korea was preparing for an imminent long-range missile test.

The official said the assessment after Kim's speech was that North Korea believes it does not have to rush to test an intercontinental ballistic missile, though shorter-range missile or engine tests could be possible at any time.

U.S. President Donald Trump--who in 2018 became the first American leader to meet with a North Korean leader--said after Kim's remarks that the North Korean leader had signed a denuclearization contract and Trump thought Kim was a "man of his word."

Last month, Pyongyang warned Washington of a possible "Christmas gift" after Kim gave the United States until the end of the year to propose new concessions in talks over his country's nuclear arsenal.

Speaking with reporters on Thursday, Chairman of the Joint Chiefs of Staff General Mark Milley said that the alert status of American forces was at a sufficient level to respond to anything that happens and military defensive capabilities were adequate to defend the United States.