Tensions continue to escalate on the Korean Peninsula, with both sides trading allegations and South Korea seizing a North Korean fishing boat that strayed into its waters.
The South Korean military Thursday said the ship sailed nearly two kilometers south of the maritime border and refused warnings to return to the North.
The three crewmembers have been taken into custody while officials in Seoul conduct an investigation. Officials say the men do not appear to be trying to defect and want to go home.
Meanwhile, North Korea has made a blistering verbal attack on South Korean President Park Geun-hye, calling her a "faithful servant and stooge" of the U.S. and comparing her to a "blabbering" peasant woman.
South Korea's Unification Ministry spokesman Kim Eui-do said the verbal attack, published Thursday by the official Korean Central News Agency, violates a recent agreement between Seoul and Pyongyang to avoid slandering each other in public comments.
"We find the comments deeply regrettable and lacking most basic civilities. We firmly call on North Korea not to repeat such rude violations (of an inter-Korean agreement)."
But Koh Yoo-hwan, a professor at Dongguk University, says Pyongyang is making the same claim against the South.
"North Koreans took [Ms.] Park's comments as slander against them and they say it is a violation of the inter-Korean agreement."
The North says the attack was in response to Ms. Park's speech this week at a nuclear summit at The Hague, where she warned Pyongyang's nuclear material could wind up in the hands of terrorists or spark a colossal nuclear accident.
A North Korean government spokesman called the speech "dumb," saying Ms. Park should stop "rambling recklessly" if she wants improved relations. He also said the comments "violently trample" the agreement to stop slandering each other.
That deal was reached last month during rare, high-level government talks. It also came just before the two sides resumed reunions between families separated by the 1950s Korean War, meetings that had not been held since 2010.
Since then, both countries have made bold moves to demonstrate their military capabilities.
On Thursday, South Korean and U.S. troops began a large-scale amphibious landing drill off the southeast coast of the Korean peninsula. Nearly 15,000 troops are taking part in the drill known as Ssang Yong, or Double Dragon, which is the largest of its kind since 1993.
The 12-day landing drill is part of wider annual joint military exercises, known as Foal Eagle, which are set to last through April 18. Washington and Seoul say the drills are defensive, but Pyongyang says it views them as preparation to invade.
In its own show of military might, the North has test-fired a flurry of rockets. The latest launch occurred Wednesday, when the North launched two mid-range Rodong missiles capable of striking Japan.
The U.S., South Korea, and Japan have condemned the launch as a violation of United Nations Security Council resolutions prohibiting North Korea from testing ballistic missiles.
The Security Council on Thursday plans to hold special a closed-door meeting to discuss a possible condemnation of the launch. Some diplomats have called for additional sanctions on the North.
In the past, North Korea has responded to such moves by carrying out nuclear tests. It has completed three nuclear tests since 2006.
South Korea's defense ministry said Wednesday it is monitoring the North for any signs of another nuclear test, but said none appeared to be imminent.
(This report was produced in collaboration with the VOA Korean service.)