– U.S. intelligence analysts are scrutinizing a newly modified North Korean satellite launch facility but see no imminent threat despite the reclusive government's latest threats of nuclear attack against the United States.

U.S. officials say North Korean crews have upgraded the Sohae Satellite Launching Station in recent months by building new rail tunnels to move equipment and new buildings where a long-range ballistic missile could be assembled.

"The goal is to prevent us from seeing what they're doing," said a U.S. official, who was not authorized to speak publicly on the intelligence assessments. "Stealth has been central to each facet of the new design."

The launch facility is about a two-hour drive from Yongbyon, North Korea's major facility for producing nuclear bomb fuel. State media announced Tuesday that "normal operation" had restarted at Yongbyon, which had been partly deactivated under a 2007 international agreement.

U.S. intelligence officials have built a tabletop model of Sohae based on satellite imagery. They say the gantry tower appears more than 200 feet tall and could accommodate a larger rocket or missile than the country has launched in the past.

"The technology they use on their rockets is nearly the same as what's used" on an intercontinental ballistic missile, the U.S. official said. "That's what has our attention."

On Tuesday, North Korea threatened to use nuclear weapons at "any time" against the U.S. because of its "reckless hostile policy."

U.S. analysts don't believe the threat is serious, and South Korea's Defense Ministry said it had not detected preparations for a missile launch.

But U.S. officials are concerned that Kim Jong Un's government has made progress toward building a smaller nuclear warhead and a missile that could carry it outside the region.

In December 2012, North Korea launched a three-stage rocket that placed a crude satellite into orbit. Two months later, it conducted a third underground nuclear blast test.

Pyongyang previously has timed nuclear tests and missile launches to coincide with major political anniversaries. This year, Oct. 10 marks the 70th anniversary of the founding of the ruling party, and U.S. intelligence analysts are watching for a possible missile test that day.