South Korea on Monday staged an air exercise near the inter-Korean border in response to an announcement from North Korea that it would launch a military reconnaissance satellite within the next seven days.

According to South Korea’s Joint Chiefs of Staff, the drills involving some 20 fighter jets -- including F-15Ks, KF-16s and the stealth F-35As -- were carried out in the skies south of the no-fly zone from around 1 p.m.

Col. Lee Sung-jun, the South Korean JCS spokesperson, said in a press briefing Monday that North Korea would be violating United Nations Security Council resolutions with its announced launch of what would be its second reconnaissance satellite.

“North Korea has told international organizations of its plans to launch a so-called military reconnaissance satellite on this day. As this is an act of provocation that violates UN Security Council resolutions, our military will take steps to demonstrate our capabilities,” he said.

He added that South Korea was closely working with the US and Japan to monitor and track North Korea’s possible satellite launch.

The North Korean announcement came just before the trilateral summit of South Korea, Japan and China in Seoul on Monday. The Japanese Kyodo News agency, citing Japan’s coast guard, said in a report that Pyongyang informed Tokyo of its plan to launch a space rocket carrying the satellite before June 3.

Three days prior on Friday, the South Korean military also warned that it had detected increased activities in North Korea suggesting possible signs of an imminent satellite launch.

On the possibility of North Korea taking other forms of provocations, such as the firing of intercontinental ballistic missiles, the JCS said that the South Korean military was “fully prepared for” either scenario.

“I would say that we are at full preparedness, for a reconnaissance satellite and missiles being launched at the same time,” Lee said. “The military is prepared for a kind of possibilities, and we are maintaining that level of preparedness and readiness.”

The presidential office made a similar assessment in a closed-door briefing to reporters on Sunday that North Korea may launch ICBMs alongside a reconnaissance satellite.

“We understand that North Korea’s launch of a satellite using ICBM technology or ICBMs themselves may be imminent,” the official said.

“There is also a possibility of other missile launches happening simultaneously, so our government will thoroughly prepare for security and defense readiness during and after the South Korea-Japan-China summit.”

South Korean military authorities believe Russian help was behind the successful launch of North Korea’s first spy satellite last November. The launch succeeded after two failed attempts earlier in the same year.

After his summit with North Korean leader Kim Jong-un last September, Russian President Vladimir Putin said he would help North Korea with its space program.

South Korea has two military reconnaissance satellites, the first one sent to space last December and the second last month.