North Korea warned the United States on Saturday to end its "military hysteria" or face retaliation as a U.S. aircraft carrier group steamed towards the region and the reclusive state marked the "Day of the Sun", the 105th birth anniversary of its founding father.

Concern has grown since the U.S. Navy fired Tomahawk missiles at a Syrian airfield last week in response to a deadly gas attack. That raised questions about U.S. President Donald Trump's plans for North Korea, which has conducted several missile and nuclear tests in defiance of U.N. and unilateral sanctions.

The North's warning came as leader Kim Jong Un, looking relaxed in a dark suit and laughing with aides, oversaw a military parade at Pyongyang's main Kim Il Sung square, named after his grandfather, on his birth anniversary.

Goose-stepping soldiers and marching bands filled the square, next to the Taedonggang River that flows through Pyongyang, in the hazy spring sunshine, followed by tanks, multiple launch rocket systems and other weapons.

Single-engine propeller-powered planes flew in a 105 formation overhead.

North Korea, still technically at war with the South after their 1950-53 conflict ended in a truce but not a treaty, has on occasion conducted missile or nuclear tests to coincide with big political events and often threatens the United States, South Korea and Japan.

"All the brigandish provocative moves of the U.S. in the political, economic and military fields pursuant to its hostile policy toward the DPRK will thoroughly be foiled through the toughest counteraction of the army and people of the DPRK," the KCNA state news agency said, citing a spokesman for the General Staff of the Korean People's Army.

DPRK stands for the official name of North Korea, the Democratic People's Republic of Korea.

"Our toughest counteraction against the U.S. and its vassal forces will be taken in such a merciless manner as not to allow the aggressors to survive."

"COMMITMENT TO MISSILES"

KCNA said the Trump administration's "serious military hysteria" had reached a "dangerous phase which can no longer be overlooked".

The United States has warned that a policy of "strategic patience" with North Korea is over. U.S. Vice President Mike Pence travels to South Korea on Sunday on a long-planned 10-day trip to Asia.

State TV showed North Korea's Pukkuksong submarine-launched ballistic missiles (SLBM) on parade with tanks and other heavy machinery in front of Kim Jong Un. It was the first time North Korea had shown the missiles, which have a range of over 1,000 km (600 miles), at a military parade.

Displaying more than one of the missiles indicates North Korea is progressing with its plan to base a missile on a submarine, which are hard to detect, said Joshua Pollack, editor of the Washington-based Nonproliferation Review. 

"It suggests a commitment to this programme," said Pollack. "Multiple SLBMs seems like a declaration of intent to advance the programme".

Choe Ryong Hae, a close aide to Kim, addressed the packed square and reiterated the warning to the United States.

"If the United States wages reckless provocation against us, our revolutionary power will instantly counter with annihilating strike, and we will respond to full-out war with full-out war and to nuclear war with our style of nuclear strike warfare," he said.

China, North Korea's sole major ally and neighbour which nevertheless opposes its weapons programme, on Friday again called for talks to defuse the crisis.

North Korea on Friday denounced the United States for bringing "huge nuclear strategic assets" to the region as the USS Carl Vinson strike group with a flag-ship nuclear-powered aircraft carrier steamed closer.