President Moon Jae-in warned North Korea on Monday not to use joint military exercises between South Korea and the United States as a pretext for provocations, saying the maneuvers are purely defensive.

Moon made the remark during a Cabinet meeting as the allies kicked off the annual Ulchi Freedom Guardian exercise that the communist nation has long denounced as a rehearsal for an invasion of the northern country.

"The Ulchi exercise is a defensive drill conducted annually. We have no intention at all to raise tensions on the Korean Peninsula," Moon said. "The Ulchi exercise is aimed at checking on defense readiness aimed at protecting the lives and property of our people."

Moon also said the North shouldn't use the exercise "as a pretext for aggravating the situation."

"North Korea must understand that it is because of its repeated provocations that South Korea and the US have to conduct defensive exercises, which in turn keeps the vicious cycle going," he said.

Moon said the current situation is more grave than ever before.

"I earnestly hope to prevent a war from breaking out again in this land and to keep peace," Moon said. "The government will make all efforts to make sure that the current situation doesn't escalate into the crisis of war while working with the international community based on the strong Korea-US alliance."

The president stressed the importance of strong defense capabilities to ensure peace.

"The government and the military must be fully ready to strongly counter any provocation," he said, according to his spokesman Park Soo-hyun.

"The president also requested the joint forces of South Korea and the United States to be fully ready to immediately and firmly repulse any provocation from the North while maintaining strong defense readiness," the spokesman told a press briefing.

Still, Moon said the doors for dialogue with the North will always remain open.

"The president said should North Korea choose the right path, it will be able to enjoy a brighter future with the cooperation of the international community," Park said.

The Ulchi exercise, which is set to run through next Thursday, involves tens of thousands of South Korean soldiers. The Ministry of National Defense did not specify the number, but ministry officials said the size is similar to that of last year, roughly 50,000.

The US has reduced the number of its participating service members to 17,500 from 25,000, according to the Pentagon. The troops include some 3,000 coming from off-peninsula.

In an unusual gesture, three top US military commanders -- Pacific Command chief Adm. Harry Harris, Strategic Command head Gen. John Hyten and Missile Defense Agency Director Lt. Gen. Samuel Greaves -- will observe the command-post exercise in person. (Yonhap)