Trump downplays concerns of North Korea's 'Christmas gift': Maybe it's 'a beautiful vase' Officials are on alert this week for a potential long-range missile test.

After months of stalled nuclear negotiations and ratcheting up rhetoric, North Korea has promised to deliver a "Christmas gift" to the U.S. -- a warning that has American and South Korean officials on high alert this week for a potential long-range missile test.

But President Donald Trump dismissed those concerns Tuesday, joking that the gift could be a "beautiful vase."

"Maybe it's a nice present. Maybe it's a present where he sends me a beautiful vase, as opposed to a missile test, right? I may get him a vase -- I may get a nice present from him," he told reporters at his resort Mar-a-Lago. He added that whatever it is, the U.S. will deal with it "successfully."

Speculation has stirred about what the gift could be, including rumors of a satellite test, a solid-fuel rocket, an announced change in policy or an intercontinental ballistic missile.

If it's an ICBM, it would be the first long-range missile test in over two years, which is not only another flagrant violation of United Nations Security Council resolutions on Pyongyang, but also a breach of Kim Jong Un's personal pledge to Trump not to test such weapons.

That could mean a swift unraveling of Trump's diplomatic efforts to end North Korea's nuclear weapons program, perhaps even a return to his days of threatening "fire and fury" on "Little Rocket Man."

The threat of a test even has commercial airliners on edge. The U.S. Federal Aviation Administration issued an alert earlier this month warning of "longer-range missile test launches prior to the end of 2019, or in the early part of 2020," according to a threat analysis obtained by ABC News.

In a Dec. 3 statement, North Korea's vice minister of foreign affairs said, "What is left to be done now is the U.S. option and it is entirely up to the U.S. what Christmas gift it will select to get."

The "option" that North Korea wants is the U.S. abandoning its "hostile policies" of demanding North Korea's nuclear disarmament and refusing to provide sanctions relief until it starts to do so -- something the Trump administration says it will not do.

The ultimatum echoed one from Kim himself in April, telling Trump that he would wait until the end of the year for the U.S. to be more flexible and take a new approach to their talks. The two leaders' second summit in Hanoi, Vietnam, last February ended when Kim offered to dismantle the nuclear facility at Yongbyon in exchange for an end to U.N. economic sanctions. That would have left North Korea's secret nuclear sites and its nuclear arsenal, so Trump walked away.

The two leaders have stayed on friendly terms, meeting again in June in a historic face-to-face at the Demilitarized Zone between the Koreas. Trump tweeted on Dec. 8 that Kim "is too smart and has far too much to lose, everything actually, if he acts in a hostile way."

But with talks deadlocked, the regime's rhetoric has increasingly soured.

Earlier this month, they crossed a symbolic threshold and attacked Trump personally, calling him a "heedless and erratic old man" in a statement from Kim Yong Chol -- the former nuclear negotiator and spy chief, whose return could also represent a turn back towards belligerency.

Beyond words, North Korea has launched more than two dozen missiles, nearly all short-range except for one ballistic missile capable of being launched from a submarine in October. All of the missiles have used solid propellants, making them more flexible, harder to detect in advance, and technologically a step ahead from the liquid-fueled rockets North Korea has traditionally used.

Trump has consistently downplayed those tests as insignificant, even as they violate U.N. resolutions and threaten key allies South Korea and Japan and the tens of thousands of U.S. troops they host.

Speculation on the "Christmas gift" has focused on a long-range missile. Gen. Charles Brown, U.S. Pacific Air Forces commander, said last week that he expects "some kind of long-range ballistic missile" test.

The Pentagon will have to move assets to be prepared for the launch, taking away needed resources for higher priorities.

U.S. Indo-Pacific Commander "Admiral (Phil) Davidson now has to take strategic Naval assets off his top priority, China, in order to protect an American territory, Guam, and a state, Hawaii, from a potential missile attack," said Eric "Olly" Oehlerich, a retired Navy SEAL and ABC News national security consultant.

But launching a long-range missile would be especially provocative, risking drawing the ire of allies China and Russia and stirring U.N. condemnation. It would also leave Pyongyang with few options for escalation and could force Trump's hand to a hardline approach, according to the Korea Institute for National Unification, a South Korean think tank.

Instead, North Korea may also test a solid-fuel rocket or sea-based ballistic missile -- both of which are more difficult for U.S. intelligence to detect in advance.

Either way, U.S. officials have warned Kim against a possible launch. Chief U.S. negotiator Stephen Biegun warned last week, "To say the least, such an action will be most unhelpful in achieving lasting peace on the Korean Peninsula."

Biegun was in South Korea, Japan and China for meetings, but did not meet any North Korean counterparts. He last met a delegation in Stockholm on Oct. 4-5, but after some productive discussions, the North Koreans walked and accused the U.S. of failing to change its hardline approach.

"It is time for us to do our jobs. Let's get this done. We are here, and you know how to reach us," Biegun said in Seoul last Monday.

ABC News's Ben Gittleson, Luis Martinez, and Josh Margolin contributed to this report.