North Korea stepped up its defiant rhetoric against the U.S. on Friday and said the U.S. is making "criminal moves for igniting a war of aggression," according to a state-run outlet.

The communist state also chided calls for negotiations for denuclearization and again slammed President Donald Trump as seeking "extinction" of North Korea through "pressures and sanctioning," said the propaganda site DPRK Today.

Defense Secretary James Mattis, in remarks at the heavily fortified Demilitarized Zone border, said that he could not imagine United States ever accepting a nuclear North Korea, warning that its rapidly advancing nuclear and missile programs would undermine, not strengthen, its security.

"Our goal is not war, but rather the complete, verifiable and irreversible denuclearization of the Korean Peninsula," Mattis said. He also reiterated America's "ironclad commitment to the South Korean people."

The Navy has three carrier strike groups currently operating in the 7th Fleet region but they are not currently all in the western Pacific. The 7th Fleet region includes both the Indian and Pacific Oceans.

The current show of force in Asia waters comes just before an upcoming state visit to South Korea by Trump.

"Everybody is concerned we're posturing to go to war, but I don't see that," said David Maxwell, associate director of Georgetown University's Center for Security Studies. "I think it's important that we continue to demonstrate that we have the will and capability should North Korea conduct any kind of attack against our ally in the South."

Defense experts say the carrier-based aircraft has the ability to perform a pre-emptive strike against North Korea and fleet escort ships could fire cruise missiles. The North's new air-defense system, though, might be capable of intercepting the military aircraft and missiles.

"This gives us the ability to actually do something as opposed to other kinds of military-symbolic gestures," said Denny Roy, an Asia Pacific security expert and senior fellow at the East-West Center, a think tank in Honolulu. In the past, he said, the U.S. has tended to use symbolic flights of aircraft along the border or send a single ship near North Korea.

However, even the carriers would not be enough firepower to defeat Pyongyang if there is a full-scale war in Korea.

Maxwell, a retired Army Special Forces colonel, said the carrier strike groups "bring tremendous capability but not enough to win the war. To win the war, it's going to take the deployment of ground forces, and of course the complete mobilization of the [Republic of Korea] military."

The carrier battle groups in Asian waters comes as the Pentagon's top general — Marine Corps Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff — is in South Korea to meet with leaders of South Korea's military "to examine strategies, plans and means needed to deter any North Korean aggression," according to the Department of Defense.