Rep. Lee Jae-myung, the leader of the main opposition Democratic Party, speaks in a leadership meeting held at the National Assembly in Seoul on Friday. (Yonhap)

Opposition leader Lee Jae-myung on Friday denounced North Korea's scrapping of a military tension reduction agreement with South Korea, expressing concern that tit-for-tat actions of both sides could lead to tensions getting out of control.

The North effectively scrapped the 2018 agreement on Thursday, saying it will restore all military measures halted under the deal. The move came after the South suspended part of the agreement in protest of the North's successful launch of a military spy satellite.

"North Korea effectively declared the scrapping of the Sept. 19 military agreement and I strongly condemn this," Rep. Lee Jae-myung, chairman of the main opposition Democratic Party, said during a party leadership meeting.

Lee said the situation is dangerously escalating with both sides taking tit-for-tat actions.

"The government should not make the mistake of killing a cow while trying to fix its horn, by pulling out the safety pin of peace, just to teach the North a bitter lesson," he said.

Lee also claimed that Russia could have decided to help with the North's satellite launch due to Seoul's hostile stance on Moscow.

The National Intelligence Service said Thursday that the North is believed to have successfully placed the satellite into orbit thanks to technological assistance from Russia in the wake of a summit between Russian President Vladimir Putin and North Korean leader Kim Jong-un. (Yonhap)