SEOUL -- The United States air force's nuclear-capable B-2 stealth bombers carried out its first-ever firing drill over the Korean Peninsula on Thursday, the Combined Forces Command said, sending another strong warning to North Korea, which has threatened a preemptive nuclear attack on the U.S. and South Korea.
   
The U.S. Strategic Command sent two B-2 Spirit Bombers for "a long-duration, round-trip training mission" from Whiteman Air Force Base in the U.S. state of Missouri to South Korea in a demonstration of the country's defense of South Korea and to provide "extended deterrence to its allies in the Asia-Pacific region," the CFC said in a release.
   
The drill was part of the ongoing bilateral Foal Eagle training exercise, which began on March 1 and will run through April 30, to test the combat readiness of the allies.    

The B-2 stealth bombers' mission involves dropping munitions and then returning to its base in a single, continuous flight ranging over 6,500 miles, the CFC said. 

"The United States is steadfast in its alliance commitment to the defense of the Republic of Korea, to deterring aggression, and to ensuring peace and stability in the region," the CFC said in a release. "The B-2 bomber is an important element of America's enduring and robust extended deterrence capability in the Asia-Pacific region." 
 
The latest move comes after North Korea's military earlier this week put its strategic rocket units on combat ready status, with a fresh threat to strike targets in South Korea as well as the U.S. mainland, Hawaii and Guam.
   
The bomber, built by U.S. aerospace firm Northrop Grumman, has a crew of two and can drop up to 230-class Joint Direct Attack Ammunition (JDAM) GPS-guided bombs.    

"As the B-2 has radar-evading stealth function, it can penetrate the anti-aircraft defense to drop conventional and nuclear weapons," a senior military official said. "It is the strategic weapon most feared by North Korea."
   
It is not the first time the U.S. military has unveiled its nuclear-capable weapons deployed from overseas bases to the peninsula during this year's joint exercises. Also taking part from the U.S. were U.S. B-22 bombers and a nuclear submarine USS Cheyenne (SSN 773), both of which are capable of deploying nuclear weapons.
   
The latest move comes after U.S. Deputy Defense Secretary Ashton Carter promised to provide all possible resources to provide extended nuclear deterrence on the peninsula during his visit to Seoul earlier this month.
   
The U.S. nuclear triad is composed of heavy bombers, intercontinental-range ballistic missiles, and submarine-launched ballistic missiles.
   
Under a new joint operational plan recently signed between the two allies, the South Korean military can ask the U.S. forces to provide reinforcements from within and outside of South Korea, including Japan and elsewhere in the region under the control of the U.S. Pacific Command, if North Korean provocations escalate.
   
About 28,500 American forces are stationed in South Korea as the 1950-53 Korean War ended in a truce, not a peace treaty. (Yonhap News)