North Korea will immediately launch a military strike in response to any provocation, Kim Yo Jong, the powerful sister of leader Kim Jong Un, said on Sunday.

The remarks come after South Korea’s military said the North had fired more than 60 artillery rounds on Saturday near their disputed maritime border, following a similar volley of more than 200 the previous day.

North Korea was firing shots again on Sunday, South Korea’s Yonhap news agency reported, citing the South’s military.

“I make myself clear once again that the safety catch of trigger of the Korean People’s Army (KPA) had already been slipped,” Kim Yo Jong said in a statement carried by state news agency KCNA.

“As already declared, the KPA will launch an immediate military strike if the enemy makes even a slight provocation,” Kim said, using the official name of the North Korean army.

Although South Korea held its own fire drills in the sea on Friday in response to the artillery shells, Yonhap said there was no plan to do so after Saturday’s events.

Friday’s duelling drills sparked warnings for residents of South Korean border islands to seek cover in bomb shelters, although there were no reports of shells crossing the maritime border.

In the statement, Kim denied the Saturday firing and said the North had detonated explosives as a deception.

South Korea’s military rejected Kim’s statement as low-level psychological warfare, urging North Korea to cease military activity that raises tension near the border.