North Korea has begun moving its mid-range missile launchers, possibly indicating a looming test as tensions are already boiling on the peninsula, U.S. officials told Fox News.
Earlier Thursday, South Korea said North Korea moved a missile with "considerable range" to its east coast after an unnamed spokesman for the North Korean army warned the U.S. Wednesday that its military has been cleared to wage an attack using "smaller, lighter and diversified nuclear" weapons.

South Korean Defense Minister Kim Kwan-jin dismissed reports in the Japanese and South Korean media that the missile could be a KN-08, which is believed to be a long-range missile that if operable could hit the United States.
Kim told lawmakers at a hearing that the missile's range is considerable but not far enough to hit the U.S. mainland. He said he did not know the reasons behind the missile movement, saying it "could be for testing or drills."
The range he described could refer to a mobile North Korean missile known as the Musudan, which has a range of 1,800 miles. That would make Japan and South Korea potential targets, but little is known about the missile's accuracy.
North Korea has railed for weeks against joint U.S. and South Korean military exercises taking place in South Korea and has expressed anger over tightened sanctions for a February nuclear test.
U.S. National Security Council spokesperson Caitlin Hayden has called North Korea's threats "unhelpful and unconstructive."
"It is yet another offering in a long line of provocative statements that only serve to further isolate North Korea from the rest of the international community and undermine its goal of economic development," she said. "North Korea should stop its provocative threats and instead concentrate on abiding by its international obligations."
Russia said Thursday that North Korea's disregard for the U.N. sanctions is hurting the chances of resuming stalled six-party nuclear talks, Reuters reports.
"Attempts by Pyongyang to violate ... decisions of the U.N. Security Council are categorically unacceptable," Foreign Ministry spokesman Alexander Lukashevich said during a briefing.
Despite North Korea's rhetoric, analysts say they do not expect a nuclear attack, which knows the move could trigger a destructive, suicidal war that no one in the region wants.
But following through on one threat Wednesday, North Korean border authorities refused to allow entry to South Koreans who manage jointly run factories in the North Korean city of Kaesong.
Washington calls the military drills, which this time have incorporated fighter jets and nuclear-capable stealth bombers, routine annual exercises between the allies. Pyongyang calls them rehearsals for a northward invasion.
The foes fought on opposite sides of the three-year Korean War, which ended in a truce in 1953. The divided Korean Peninsula remains in a technical state of war six decades later, and Washington keeps 28,500 troops in South Korea to protect its ally.
U.S. Defense Secretary Chuck Hagel said Washington was doing all it can to defuse the situation, echoing comments a day earlier by Secretary of State John Kerry.
"Some of the actions they've taken over the last few weeks present a real and clear danger and threat to the interests, certainly of our allies, starting with South Korea and Japan and also the threats that the North Koreans have leveled directly at the United States regarding our base in Guam, threatened Hawaii, threatened the West Coast of the United States," Hagel said Wednesday.
The Pentagon said in Washington that it will deploy a missile defense system to the U.S. Pacific territory of Guam to strengthen regional protection against a possible attack.
In Pyongyang, the military statement said North Korean troops had been authorized to counter U.S. "aggression" with "powerful practical military counteractions," including nuclear weapons.
"We formally inform the White House and Pentagon that the ever-escalating U.S. hostile policy toward the DPRK and its reckless nuclear threat will be smashed by the strong will of all the united service personnel and people and cutting-edge smaller, lighter and diversified nuclear strike means," an unnamed spokesman from the General Bureau of the Korean People's Army said in a statement carried by state media, referring to North Korea by its formal name, the Democratic People's Republic of Korea. "The U.S. had better ponder over the prevailing grave situation."
However, North Korea's nuclear strike capabilities remain unclear.
Pyongyang is believed to be working toward building an atomic bomb small enough to mount on a long-range missile. Long-range rocket launches designed to send satellites into space in 2009 and 2012 were widely considered covert tests of missile technology, and North Korea has conducted three underground nuclear tests, most recently in February.
"I don't believe North Korea has to capacity to attack the United States with nuclear weapons mounted on missiles, and won't for many years. Its ability to target and strike South Korea is also very limited," nuclear scientist Siegfried Hecker, a senior fellow at the Center for International Security and Cooperation at Stanford University, said this week.
"And even if Pyongyang had the technical means, why would the regime want to launch a nuclear attack when it fully knows that any use of nuclear weapons would result in a devastating military response and would spell the end of the regime? " he said in answers posted to CISAC's website.
In Seoul, a senior government official said Tuesday that it wasn't clear how advanced North Korea's nuclear weapons capabilities are. But he also noted fallout from any nuclear strike on Seoul or beyond would threaten Pyongyang as well, making a strike unlikely. He spoke on condition of anonymity because he wasn't authorized to speak publicly to the media.
North Korea maintains that it needs to build nuclear weapons to defend itself against the United States. On Monday, North Korean leader Kim Jong Un led a high-level meeting of party officials who declared building the economy and "nuclear armed forces" as the nation's two top priorities.
Fox News' Justin Fishel and the Associated Press contributed to this report.