"There is sufficient room for dialogue (with North Korea) as to the pullout of US troops," Sim said in response to a question of how she would respond if the communist regime demands it as a condition for an inter-Korean peace declaration.

"The reason why the North is adhering to its nuke program is its own survival ... What is at the core of this issue is not the withdrawal of US troops, but the North's demand for the security of its regime," Sim added.

Pyongyang has long called for a peace treaty that will end the armistice agreement that brought a halt to the 1950-53 Korean War.

Critics here say that the North's call is intended to remove US troop presence here and Washington's nuclear protection for Seoul, and to stop the allied military drills.

During the debate, Sim also pointed out that as the South Korea-US alliance has been evolving to provide broader regional security beyond its traditional role of deterring the North, it does not need to be seen as "static" for only peninsular defense.

"We can sufficiently discuss (this issue with the North) and reach an agreement on a solution," Sim said.

Though she recognized the alliance with the US as the "very important, irreplaceable" asset for the security of South Korea, Sim stressed the need to overcome "old views" about the security partnership.

"Some people mistakenly believe that the alliance means we have to be depending on or clinging to the US We have to get over such old views," she said.

Sim also criticized Washington for the recent unannounced delivery of the key components of a US missile defense system to a southeastern county, stressing that it is an "act that ignores the sovereignty of its ally."

"I express my strong regret to the US," she said, calling the delivery "abnormal."

"If elected president, I will let (the issue) go through the due procedures (of securing public consent) and reconsider the deployment."

On Wednesday, the US forces brought the radar and other equipment of a Terminal High-Altitude Area Defense battery to Seongju, 296 kilometers southeast of Seoul, in what critics say was a hurried move ahead of the May 9 presidential election here. (Yonhap)