Rep. Chung Jin-suk, the interim chief of the ruling People Power Party, speaks at a party emergency response meeting in the southern city of Daegu, Oct. 13. Yonhap

Ruling party leader Chung Jin-suk called Thursday for significantly bolstering the U.S. nuclear umbrella for South Korea to cope with intensifying nuclear threats from North Korea.

Chung issued the call a day after he called for scrapping a 1991 inter-Korean declaration on denuclearization, stressing that strengthening the alliance with the U.S. is the only feasible option to deter the North.

"It should not be overlooked that North Korea's recent missile provocations involve not just ballistic missiles but 'tactical nuke' simulations," Rep. Chung of the People Power Party (PPP) said. "We need to take all necessary measures in terms of defense and security."

"Reinforcing the South Korea-U.S. military alliance like an iron wall is the only solution. We need to dramatically strengthen the U.S. extended deterrence, or the nuclear umbrella, and these matters should be discussed as central issues between the two countries."

Calls have grown in South Korea for the redeployment of U.S. tactical nuclear weapons or the country's own nuclear armament as the North has sharply escalated threats with a series of missile launches that Pyongyang said simulated nuclear missile strikes on the South.