The United States warned Wednesday it will use military force -- if necessary -- against the growing nuclear threat from North Korea, following the communist nation's Fourth of July test launch of an intercontinental ballistic missile capable of reaching North America. 

North Korea's leader, Kim Jung Un, had kept his country's first intercontinental ballistic missile (ICBM) hidden from spy satellites until just before it was rolled into launch position and aimed into space.  Powered by a two-stage rocket engine, it flew for 37 minutes on Tuesday.  The missile could have reached Alaska, had it been aimed in that direction, CBS News' David Martin reports from the Pentagon. 

Leon Panetta CBS News

"There's no question we've crossed a threshold here in the North Koreans' ability to develop an ICBM," Leon Panetta, former CIA director and defense secretary during the Obama administration, told CBS News. " It represents a very serious national security threat to the United States." 

U.S. intelligence first identified it as just an intermediate range missile, which perhaps explained President Trump's initial, rather flip reaction -- a tweet apparently asking about Kim Jong Un, Martin reports. 

"Does this guy have anything better to do with his life?"  Mr. Trump tweeted. 

North Korea has just launched another missile.  Does this guy have anything better to do with his life?  Hard to believe that South Korea..... — Donald J. Trump (@realDonaldTrump) July 4, 2017

But David Wright of the Union of Concerned Scientists did his own calculations and got it right: the missile could have flown more than 4,000 miles. 

"I've been watching North Korea for a long time and I'm surprised by how fast they've been able to pull out new missile designs, launch them and despite having some failures do relatively well," Wright told CBS News. 

David Wright CBS News

Wright estimates it would take North Korea another couple years to develop an ICBM that could send a 1,000-pound nuclear warhead hurtling toward the U.S., but unless something happens, the day when North Korea will have that capability is coming. 

"We're going to see them reach that point and it may be sooner rather than later," Wright said. 

The U.S. and South Korea responded to the latest test with some missile launches of their own, but Panetta says it will take more than shows of force to change Kim Jung Un's mind. 

"You can't out-bully a bully in North Korea," Panetta said. " So it doesn't make a lot of sense to simply sit back and threaten this leader." 

North Korean leader Kim Jong Un reacts with scientists and technicians of the DPRK Academy of Defence Science after the test-launch of the intercontinental ballistic missile Hwasong-14 in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang on Wed., July 5, 2017.  KCNA/Reuters

The Pentagon could make good on its threats, Martin reports, but nobody from the secretary of defense on down favors military action, which they say could lead to catastrophic loss of life on the Korean Peninsula. 

At an emergency meeting of the U.N. Security Council Wednesday, Ambassador Nikki Haley said the U.S. will propose tougher sanctions against North Korea, CBS News' Ben Tracy reports from Beijing.  This includes restricting oil imports and cutting off sources of hard currency. 

"Today is a dark day," Haley said. " It is a dark day because [Tuesday's] actions by North Korea made the world a more dangerous place... North Korea's launch of an ICBM is a clear and sharp military escalation." 

Chinese President Xi Jinping and Russian President Vladimir Putin met in Moscow and announced that they oppose any use of force against North Korea or sanctions that would strangle its economy. 

China is North Korea's main ally and accounts for more than 80 percent of its trade.  To pressure the North into ending its missile tests China has stopped buying North Korean coal.  But it has not cut off oil shipments to North Korea fearing that could cause Kim Jong Un's regime to collapse causing the Korean Peninsula to destabilize. 

Jeffrey Lewis is an expert on nuclear policy.  He says without a coordinated international response, tough talk and sanctions are the only realistic weapons the U.S. has to fight North Korea. 

Jeffrey Lewis CBS News

"The Russians and the Chinese just don't care… it's not their problem," Lewis told CBS News. " So I would expect that cycle to repeat, they'll be condemned, they'll be angry about it, they'll do a nuclear test and we'll be back to square one again.  Later, rinse, repeat." 

China and Russia are calling on North Korea to halt its missile and nuclear tests, Tracy reports, but in exchange they want the U.S. and South Korea to end their joint military exercises in the region.  The U.S. isn't likely to agree to that. 

President Trump, who is in Poland on the first stop on a trip that will take him to the G20 summit in Germany this week -- is now looking at ways to cut off North Korea's financial lifeline without Beijing's help, CBS News' Margaret Brennan reports. 

Despite Mr. Trump's very public attempts to befriend President Xi Jinping -- including at his Mar-a-Lago resort -- Beijing remains strongly opposed to action that would destabilize Kim Jong Un's regime. 

Mr. Trump said Wednesday, "So much for China working with us," ahead of a planned meeting this week with President Xi. 

Ahead of Mr. Trump's meeting with Putin at the G20, pressure has been added to the already high stakes one-on-one, Brennan adds.  Mr. Trump does not have diplomatic experience, and squaring off with President Putin -- a highly experienced operator -- is new territory. 

The White House said there's no agenda for the meeting but it comes amid multiple investigations into Russian meddling in the U.S. election.  It's unclear if Mr. Trump will confront Putin about that, Brennan reports.