Tension has been rising in recent weeks as Pyongyang has conducted a series of weapons tests and waged a war of words with U.S. President Donald Trump.
"I remain hopeful that we could again get the process started again and remain on the diplomatic path," Esper told reporters at the Pentagon during a briefing.
Chinese Vice Foreign Minister Le Yucheng met U.S. special envoy for North Korea Stephen Biegun on Friday.
Esper also noted that along with supporting diplomats, he must "ensure the we are in a high state of readiness, prepared to fight and win, tonight if need be. And I'm confident in that."
"We are prepared for whatever," Chairman of the Joint Chiefs of Staff General Mark Milley said during the same briefing, but declined to discuss specific intelligence.
Experts say North Korea could restart intercontinental ballistic missile (ICBM) testing suspended since 2017.
Such a test would mark a break from the detente reached with the United States last year, dash any hopes of resuming talks on ending North Korea's nuclear and missile programs and put the two countries back on a path of confrontation.