President Yoon Suk Yeol called for bolstering readiness against North Korea's "gray zone" provocations and hybrid warfare as South Korea and the United States kicked off their annual joint exercise on Monday.

Yoon said during a Cabinet meeting that this year's Ulchi Freedom Shield exercise will focus on integrating the allies' capabilities under various crisis scenarios to deter North Korea's evolving military threats, psychological warfare and cyberattacks.

"We must strengthen our readiness to respond to North Korea's gray-zone provocations, such as the spread of false information, fake news and cyberattacks," Yoon said. "Anti-state forces that threaten the free democracy are operating covertly in various places."

Yoon warned that the North might seek to create social instability through violence, propaganda and agitation at the early stages of a conflict.

"We must actively seek methods to block division and raise people's resolve to resist," Yoon said. "To maintain national security and raise our war preparedness, we must firmly protect transportation, communication, water, social infrastructure, and critical national facilities."

The Ulchi Freedom Shield, set to run until Aug. 29, features computer-simulated war games and field training, while the Seoul government conducts civil defense drills from Monday through Thursday.

On the first day of the exercise, Yoon presided over a National Security Council meeting with Cabinet members and Joint Chiefs of Staff Chairman Adm. Kim Myung-soo to assess the government and military's preparedness and contingency plans, his office said.

Seoul and Washington have said their drills are defensive in nature, but Pyongyang has long denounced the allies' joint exercises as a rehearsal for an invasion against it and has a track record of staging weapons tests in response.

On Sunday, the Institute for American Studies of the North Korean foreign ministry condemned the Ulchi exercise as the "most offensive and provocative war drills for aggression."

Tension remain high as the North has flown thousands of balloons loaded with trash across the border in a tit-for-tat move against South Korean civic groups' sending of balloons carrying anti-Pyongyang propaganda leaflets into the North. (Yonhap)