South Korea's military said it believed missiles displayed in a North Korean military parade included new types of intercontinental ballistic missiles (ICBM).

The North's leader, Kim Jong-un, attended the parade in the capital, Pyongyang, as a series of missiles, multiple launch rocket systems and rockets were on display, amid questions about U.S. plans for the country and concerns about a possible sixth nuclear test.

Earlier Saturday, North Korea warned the United States to end its "military hysteria" or face retaliation as a U.S. aircraft carrier group steamed toward the region and the reclusive state marked the 105th anniversary of the birth of its founder and the current leader's grandfather, Kim Il-sung.

'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.' - Korean People's Army spokesperson

Concern has grown since the U.S. Navy fired 59 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 missile and nuclear tests in defiance of UN and unilateral sanctions. 

The North's warning, carried by its state-run KCNA news agency, came as leader Kim Jong-un arrived at Pyongyang's main Kim Il-sung Square, named after his grandfather, for a military parade marking the "Day of the Sun."

North Korea Founder's Birthday

North Korean leader Kim Jong-un applauds during Saturday's parade in Pyongyang celebrating the birthday of his late grandfather and North Korea founder Kim Il-sung. (KRT/Associated Press)

Goose-stepping soldiers and marching bands filled the square in the hazy spring sunshine as tanks, multiple launch  rocket systems and other weapons waited to parade.

CBC's Saša Petricic was in Pyongyang, travelling with a government representative, as he watched the choreographed display of military might.

"You can feel the ground shake with every one of these platoons that go by. If you look to the other side (of the square), you can see rows and rows of senior officers who are clapping in unison," he said.

North Korea Founder's Birthday

North Korea parades never-before-seen missiles across Kim Il Sung Square during a military parade on Saturday. (Wong Maye-E/Associated Press)

"This is meant to show a level of defiance form North Korea."

 A series of what appeared to be KN-08 missiles were among the weapons rolled out on trucks. Analysts say the missiles could one day be capable of hitting targets as far as the continental United States, although North Korea has yet to flight test them.

The parade also included large rockets covered by canisters in two different types of transporter erector launcher trucks, or TELs, which can carry, move into launch position and fire missiles. An official from South Korea's Defense Ministry couldn't immediately confirm whether any of the rockets represented a new type of ICBM.

Kim Dong-yub, a North Korea expert at Seoul's Institute for Far Eastern Studies, said the canisters and trucks suggested that the North was developing technology to "cold launch" ICBMs, ejecting them from the canisters before they ignite. This would allow North Korea to launch its missiles without damaging its limited number of ICBM-capable launcher trucks and also make the missiles harder to detect after they're fired, he said. Cold launches would also allow the missiles to be fired from silos.

Kim, the analyst, said it's likely that North Korea is also developing solid-fuel ICBMs, and that some of the rockets inside the canisters on Saturday might have been prototypes. 

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.

North Korea Founder's Birthday

In this image taken from video aired by North Korean broadcaster KRT, a portrait of Kim Il-sung is carried during a parade at the square named for him in Pyongyang on Saturday. (KRT/Associated Press)

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

"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." 

'Open threat' 

The state news agency 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. 

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

North Korea military parade

The military parade, celebrating the 105th anniversary of the birth of Kim Jong-un's grandfather, was held amid rising tensions over North Korea's missile tests. (CBC)

"We call on all parties to refrain from provoking and threatening each other, whether in words or actions, and not let the situation get to an irreversible and unmanageable stage," Chinese Foreign Minister Wang Yi told reporters in Beijing. 

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 flagship nuclear-powered aircraft carrier steamed closer, and said it stood ready to strike back. 

"The Trump administration, which made a surprise guided cruise-missile strike on Syria on April 6, has entered the path of open threat and blackmail," KCNA quoted the military as saying in a statement. 

"The army and people of the DPRK will as ever courageously counter those who encroach upon the dignity and sovereignty of the DPRK and will always mercilessly ravage all provocative options of the U.S. with Korean-style toughest counteraction."

With files from CBC News and The Associated Press