The agreement came at a telephone conversation between Chung Eui-yong, the head of South Korea's Presidential National Security Office, and his U.S. counterpart H.R. McMaster.
The two "discussed current security conditions surrounding the Korean Peninsula caused by North Korean provocations and heightened tension, and ways to deal with such threats," Cheong Wa Dae spokesman Park Soo-hyun told a press briefing.
"The two sides reaffirmed their promise to closely and transparently cooperate on the steps to be taken in each stage to help ensure the security and safety of both South Korea, the United States and their people."
The telephone conversation started at 8 a.m. (Seoul time) and lasted 40 minutes.
Rejecting the new U.S.-proposed sanctions resolution adopted earlier this week by the U.N. Security Council, Pyongyang said it would consider a plan for a missile strike around the U.S.-controlled island of Guam, home to several U.S. military units.
U.S. President Donald Trump spoke of "fire and fury" from the very onset.
On Thursday (U.S. time), he refused to rule out the possibility of a pre-emptive strike against the communist state, only saying, "We don't talk about that.
"If North Korea does anything in terms of even thinking about attack of anybody that we love or we represent or our allies or us, they can be very, very nervous," he said. "Because things will happen to them like they never thought possible.", source from the Yonhap.