South Korea on Thursday fired several artillery rounds into North Korea after detecting an incoming projectile fired from the North, the South Korean Defense Ministry said.
There were no reports of casualties or damage on the South Korean side. The South has ordered the evacuation of residents from the western border area and the South Korean military has been put on its highest state of readiness, the ministry said.
Also, South Korean President Park Geun Hye was due to convene a National Security Council session.
The ministry said that South Korean military radar at 3:52 p.m. detected that an apparent rocket was fired from the North Korean side in the direction of Gyeonggi Province north of Seoul.
In retaliation, South Korea fired back "tens" of 155-millimeter shells at the location where the North Korean projectile was fired, the ministry added.
After firing the artillery, the South Korean said it had detected no response from the North, indicating that the two sides had not entered a state of combat.
If the North actually fired on the South, it would be the first time since November 2010, when it shelled a South Korean island in the Yellow Sea.
Inter-Korean tensions have been running high since South Korea accused North Korea earlier this month of planting landmines in the border area in violation of the Armistice Agreement and seriously injuring two South Korean soldiers.
The South Korean military subsequently resumed propaganda broadcasts using loudspeakers in the border area for the first time in 11 years.