The Trump administration wants North Korea to restart nuclear negotiations, White House national security adviser Robert O’Brien told news site Axios in an interview published late Sunday.

"We've reached out to the North Koreans and let them know that we would like to continue the negotiations in Stockholm that were last undertaken in early October,” O’Brien said.

U.S. and North Korea negotiators last met in October but nuclear talks fell through on the first day of meetings.

"We've been letting them know, through various channels, that we would like to get those [negotiations] back on track and to implement Chairman Kim's commitment to the denuclearization of the Korean Penninsula” O’Brien continued, referring to North Korean leader Kim Jong Un.

Washington wants North Korea to pursue a path of denuclearization, while Pyongyang wants the U.S. to lift sanctions. Nuclear negotiations began in June 2018, when President Trump met Kim for a summit in Singapore. The two leaders also met in Vietnam in February but failed to strike a deal.

North Korea said last week that it felt “deceived” by the U.S., as negotiations have stalled after 18 months.

In December, Pyongyang had threatened the U.S. with a “Christmas gift,” which some security analysts believed to be an intercontinental ballistic missile launch. North Korea did not end up conducting any aggressive military tests around Christmas, with O’Brien calling this development “encouraging.”

“All we know is we were told we were going to get a Christmas gift and the Christmas gift didn't come. And so I think that was an encouraging sign. But, again, that doesn't mean we won't see some sort of test in the future," O’Brien said.

Trump and Kim have had a friendly personal relationship, sending cordial letters to one another. This friendship between the two leaders could be one reason why North Korea hasn’t been as eager to provoke the U.S.

Pyongyang frequently shot off short-range missiles in 2019, which had threatened North Korea’s East Asian neighbors, such as Japan. Yet Trump has often dismissed the tests, calling Kim “Rocket Man.”

A possible nuclear deal between the U.S. and North Korea could be a major achievement for Trump’s presidential legacy. Yet former national security adviser John Bolton has said that North Korea would never give up its nuclear arsenal and some Democrats have slammed Trump for not being more aggressive towards Pyongyang.