Tensions escalated on the Korean Peninsula on Friday morning as North Korea fired some 200 artillery shells into the sea north of the border.

Immediately after the North fired the shells off its western coast, South Korean authorities issued evacuation orders on Yeonpyeong Island and Baekryeong Island.

North Korea continued to fire shells for two hours until 11 a.m., the South Korean military said.

The South’s military said no South Korean citizens or members of the armed forces were harmed.

In a brief release, the South Korean Joint Chiefs of Staff said that Friday’s actions by the North constituted a “resumption of artillery firing in the ‘buffer zones’ around the sea border” and “an act of provocation that escalates tensions and threatens peace on the Korean Peninsula.”

In November, North Korea announced it was withdrawing from a 2018 inter-Korean agreement aimed at minimizing military tensions near the shared border. Under the now-defunct agreement, the staging of drills and other military activities were withheld by both sides in “buffer zones.”

The JCS said the “responsibility for the escalating crisis lies with North Korea” and called for an “immediate pause.”

“We are tracking and monitoring the relevant developments in close coordination with the US and will be taking measures commensurate to North Korea’s provocations,” it said.

In an English-language statement carried by the Korean Central News Agency, the Korean People’s Army said that its drill on Friday was “a natural countermeasure” against the US and South Korea’s joint live-fire exercise which took place Thursday.

The joint exercise took place to bolster combined operational capabilities against North Korea’s military threats.

North Korea added that its armed forces will take “tough countermeasures on an unprecedented level.”