Prime Minister Chung Hong-won told lawmakers Monday that the U.S. control of South Korean troops in wartime should continue until Seoul is fully ready to deter the North’s war ambitions.

South Korea and the U.S. agreed late last month to a “conditions-based” operational control transition, citing North Korea’s growing military threat. The transfer, previously scheduled for December 2015, is expected to take place in the mid-2020s.

With no clear time frame set, opposition lawmakers and activists charge that the decision constitutes a desertion of military sovereignty and a breaking of one of President Park Geun-hye’s key election pledges.

“The government’s task is to fulfill all conditions so that the North won’t dare harbor ambitions (to invade). Given our asymmetrical warfare capabilities, it is right for us to delay the transition until the conditions are met,” Chung said at the National Assembly.

“We need to keep in mind that North Korea’s nuclear weapons are being sophisticated, and it has been carrying out missile tests recently.”

Defense Minister Han Min-koo pointed to “grave threats,” especially those posed by the communist state’s multiple rocket launchers to the Seoul metropolitan area.

During the session, Chung and Unification Minister Ryoo Kihl-jae were also grilled over the balloons with anti-North Korea leaflets sent by defectors and activists, which have riled Pyongyang as it sees them as an attempt to help topple the regime.

Liberal lawmakers and residents in border regions have been stepping up calls for the government to contain their campaign since the North fired heavy machine guns last month apparently aiming at balloons launched by the civic groups, which contained flyers denouncing the Kim dynasty, $1 bills, mini radios and other items.

Their crusade is intensifying the dilemma for Seoul over how to balance the citizens’ right to freedom of assembly and association, and its need to maintain the momentum for a cross-border thaw in the wake of a surprise visit on Oct. 4 by three top North Korean officials.

The South had proposed a fresh round of high-level dialogue on Oct. 30 but it did not materialize as the North demanded a halt to the sending of flyers as a prerequisite.

Yet Chung again upheld the government’s policy not to block any release of the leaflets, while vowing to ensure the safety of residents in border towns and minimize any social strife in the South.

“We regret that the North takes issue with the leaflets and threatens to cease dialogue, which is incomprehensible,” the prime minister added.

“There are no legal grounds to restrict the leaflets. … But we will respond with appropriate measures to any problem with the safety of our citizens or a social divide.”

By Shin Hyon-hee (heeshin@heraldcorp.com)