North Korea's army will immediately launch a "baptism of fire" in response to any provocation, Kim Yo Jong, the powerful sister of leader Kim Jong Un, said on Sunday, in comments carried by state news agency KCNA.
The remarks come after South Korea's military said the North fired more than 60 artillery rounds on Saturday near their disputed maritime border, following a similar volley of more than 200 there the previous day.
"Let me be clear once again that our army has its trigger already unlocked," Kim Yo Jong said in a statement carried by KCNA.
"Our army will immediate launch a baptism of fire in case of even a small provocation."
Although South Korea held its own fire drills in the sea on Friday in response to the artillery shells, the Yonhap news agency 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, though there was no report of shells crossing the maritime border.
In the statement, Kim denied the Saturday firing and said the North detonated explosives instead as a deception.
The Strait of Hormuz remains open to all shipping except vessels linked to "Iran's enemies", Iran's representative to the UN maritime agency was quoted as saying in Iranian media reports published on Sunday.
The Gulf Cooperation Council (GCC) has renewed its condemnation of continued Iranian attacks on member states, including the targeting of infrastructure and oil facilities, in flagrant violation of international law and a direct threat to regional security, stability and the safety of global energy supplies.
The Qatar Ministry of Interior has confirmed six people died during a helicopter crash into "regional waters" on Sunday - with search and rescue teams still searching for the body of the seventh and final crew member.
Japan could consider deploying its military for minesweeping in the Strait of Hormuz, a vital artery for global oil supplies, if a ceasefire is reached in the U.S.-Israeli war on Iran, Foreign Minister Toshimitsu Motegi said on Sunday.