A top U.S. Air Force general on Tuesday said he expects North Korea’s “Christmas gift” to the United States to be a long-range missile test, after Pyongyang delivered an ominous threat ahead of a unilateral year-end deadline for progress in nuclear talks.

“What I would expect is some type of long-range ballistic missile would be the gift,” said Gen. Charles Brown, commander of the U.S. Pacific Air Forces. “It’s just a matter of does it come on Christmas Eve, does it come on Christmas Day, does it come after the New Year.”

Brown made the remarks to U.S. media at a roundtable discussion in Washington.

Those remarks come amid rising tensions and ahead of the looming year-end deadline set by North Korean leader Kim Jong Un for the United States to lift crushing sanctions or make other concessions in the deadlocked denuclearization negotiations.

Earlier this month, a senior North Korean official threatened to deliver a “Christmas gift” to the United States, a remark that stirred concerns that Pyongyang planned to escalate its confrontation with Washington. Some analysts believe this escalation could come in the form of a satellite launch or test of an intercontinental ballistic missile (ICBM), possibly over Japan.

Alternatively, Brown said the North, which hasn’t tested an ICBM since 2017, could announce a lifting of its self-imposed moratorium on long-range missile and nuclear tests.

“I think there’s a range of things that could occur,” he said. “I think there’s also the possibility that the self-imposed moratorium may go away and nothing happens right away. (Kim) announces it but then doesn’t shoot.”

Brown said the U.S. military is preparing to respond to any North Korean provocation by reviewing the options it examined in 2017, when U.S. President Donald Trump vowed to unleash “fire and fury” on the North if it threatened the United States or its allies.

“Our job is to backstop the diplomatic efforts,” he said. “And if the diplomatic efforts kind of fall apart, we’ve got to be ready, and I can’t be studying the problem. And that’s the thing, we’re already thinking ahead. Go back to 2017, there’s a lot of stuff we did in 2017 that we can dust off pretty quickly and be ready to use.”

According to U.S. news website Military.com, Brown did not rule out the use of B-1 or B-2 strategic bombers to respond to any North Korean test.

“We’re going through all the complete options,” he was quoted as saying in response to a question about the bombers. “My job is to write this military advice and then our leadership will determine which levers they want to pull.”

Brown said the U.S. did fly bombers near North Korea in 2017 when the regime tested powerful ballistic missiles, including those capable of reaching the U.S. mainland.

“After Pyongyang tested ballistic missiles in 2017, U.S. bombers and stealth fighters paired up with South Korean fighter jets to fly near North Korea,” he said, according to the Voice of America. “We are looking at all the things we’ve done in the past.”

North Korea announced Saturday that it had conducted “another crucial test” at its Sohae long-range rocket site — the second test at the site in a week — claiming that the move would bolster its “reliable strategic nuclear deterrent.”

Kim warned in April that Pyongyang could take a “new path” if Washington does not respond sufficiently to its entreaties by the year-end. Top U.S. officials, however, have brushed off the deadline as “artificial.”

A return to ICBM launches could send U.S.-North Korea ties back to where they were in 2017, when tensions surged and analysts fretted over the possibility of military conflict. It would also undermine what Trump considers to be one of his key foreign policy achievements as he faces impeachment proceedings and his re-election campaign heats up.

In an apparent bid to stave off a worst-case scenario after China and Russia proposed lifting some U.N. sanctions on North Korea, the U.S. State Department said Tuesday that Washington’s top envoy for North Korea, Stephen Biegun, would visit Beijing for two days on Thursday and Friday “to discuss the need to maintain international unity on North Korea.”

Shortly after this announcement, the U.S. ambassador to the U.N., Kelly Craft, held out the possibility of “united action” on North Korea. It was not immediately clear if this meant Washington would relax its stance that Pyongyang must first relinquish its nuclear arsenal before any sanctions relief.

“The @UN Security Council has and should always speak in unison on North Korea. We are willing to consider united action, but it must advance the commitments @POTUS Trump and Chairman Kim made in Singapore,” Craft wrote on Twitter, referring to the two leaders’ historic first summit meeting in the city-state in June last year.

Biegun’s sudden change in itinerary comes after he visited Seoul earlier this week in a bid to salvage talks by reaching out to Pyongyang ahead of the deadline. South Korean media reported that North Korean officials did not respond to Biegun’s call for a possible meeting.

Biegun is scheduled to meet with Japanese officials in Tokyo on Wednesday before leaving the following day for Beijing.