U.S. Senate to get top-level briefing on North Korea

As the world braces for a possible North Korean nuclear test, Chinese President Xi Jinping on Monday urged restraint in a call to President Donald Trump. America's UN envoy warned of a strike if Pyongyang attacks a U.S. military base or tests an intercontinental ballistic missile.

Xi's phone call with Trump came amid signs Pyongyang could soon conduct its sixth nuclear test explosion since 2006, or the latest in a rapid series of missile tests, further advancing its ambitions of developing a nuclear-tipped missile that could reach the U.S. mainland.

In Washington, the Trump administration invited the entire 100-member Senate for a briefing Wednesday on the escalating crisis. Adding to the atmosphere of animosity, officials said North Korea has detained a third U.S. citizen.

Trump told ambassadors from UN Security Council members that the status quo in North Korea is "unacceptable" and the council must be prepared to impose additional and stronger sanctions.

"This is a real threat to the world, whether we want to talk about it or not. North Korea is a big world problem, and it's a problem we have to finally solve. People have put blindfolds on for decades, and now it's time to solve the problem," he said at the White House.

North Korea poses one the sternest national security challenges facing the 3-month-old Trump administration. The administration has settled on a strategy emphasizing increased pressure on North Korea with the help of China, rather than trying to overthrow Kim Jong-un's isolated government or use military force. But senior officials have repeatedly said that "all options" remain on the table.

Seeking common ground with China

China is a traditional ally of North Korea and fought on its side in the 1950-53 Korean War. Those ties have frayed, but Beijing remains the North's economic lifeline. The Xi-Trump call on Monday morning Beijing time was the second time the two leaders have spoken by telephone since meeting in Florida earlier this month.

Xi told Trump that China strongly opposes North Korea's nuclear weapons program, which violates UN Security Council resolutions, and hopes "all parties will exercise restraint and avoid aggravating the situation" on the Korean Peninsula, China's official broadcaster CCTV said.

A White House readout of the call said Trump criticized North Korea's "continued belligerence" and the leaders "reaffirmed the urgency of the threat." They committed to strengthening coordination to denuclearize North Korea, a statement said.

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The USS Carl Vinson aircraft carrier and ships in the strike group accompanying it are continuing to move toward the South Korea region, after completing a short naval exercise with Japanese ships in the Philippine Sea. But the ships are probably several days from arriving in the region.

In addition to the Carl Vinson, the USS Michigan, a nuclear-powered, guided-missile submarine, is due to arrive Tuesday on a routine port visit at Busan, South Korea, a U.S. defense official said. The official was not authorized to discuss the ship movement publicly so spoke on condition of anonymity.

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Tuesday marks the founding anniversary of North Korea's armed forces. It has marked such dates in the past with displays of its military capabilities.

Commercial satellite imagery suggests the North has been readying for weeks for an underground atomic explosion, and could conduct one at any time. Alternatively, a long-range missile test could show North Korean progress toward being able to fire a weapon at America. But any decision by Trump to resort to military action would be highly risky, principally because the capital of close ally South Korea lies within range of North Korea artillery and rockets.

Nikki Haley, Trump's UN ambassador, said Monday the U.S. wasn't looking for a fight with Kim and wouldn't attack North Korea "unless he gives us reason to do something." She praised China's increased pressure on North Korea.

Asked about the threshold for U.S. action, Haley told NBC's Today that "if you see him attack a military base, if you see some sort of intercontinental ballistic missile, then obviously we're going to do that."

But asked what would happen if North Korea tests an intercontinental missile or nuclear device, Haley said, "I think then the president steps in and decides what's going to happen."

White House press secretary Sean Spicer said the briefing to senators will be delivered by four top administration officials: Secretary of State Rex Tillerson, Defense Secretary Jim Mattis, Director of National Intelligence Dan Coats and the chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford.

The latest American held in North Korea is Tony Kim, who also goes by his Korean name Kim Sang-duk. The 58-year old taught accounting for a month at the Pyongyang University of Science and Technology. He was detained on Saturday, according to Park Chan-mo, the university chancellor. No details on why Kim was detained have been released.