UN Secretary-General Ban Ki-moon has warned that a small incident could provoke an "uncontrollable" situation on the Korean Peninsula.
Speaking at a news conference in Rome, the UN chief also urged North Korea to refrain from further raising tensions.
"Pyongyang authorities should look at what is happening, what is going on around the world in this era of globalization," Ban said, "and they should do more enhance the well-being and prosperity of their own people rather than increasing level of tensions, rather than taking very negative provocative measures."
Ban's warning came after North Korea urged foreigners to evacuate from South Korea, saying they could be at risk in case of war.
The warning was read by an announcer on state-run television on April 9.
"We urge all foreign nationals at institutes and companies, including tourists, to take evacuation measures out of Seoul and South Korea for their own safety," she said.
It was the latest in a series of threats made by Pyongyang in recent weeks.
Last week, North Korea said it could not guarantee the safety of foreign embassy staff in Pyongyang from April 10 and suggested evacuating the embassies.
North Korea also reportedly moved at least one midrange missile to its east coast.
In reaction to Pyongyang's threats, Japan deployed Patriot missile interceptors around Tokyo on April 9.
Also on April 9, North Korean workers failed to show up for work at an industrial park inside North Korea and run jointly with South Korea.
Pyongyang said it was halting operations at the Kaesong industrial complex and pulling out its 53,000 workers. Last week, Pyongyang blocked entry to the complex to South Koreans, allowing them only to leave.
The industrial complex was the last economic link between North and South Korea.
Tensions have been rising on the Korean Peninsula since North Korea carried out its third nuclear test last month, which led to a tightening of UN sanctions against Pyongyang.
With reporting by Reuters, AFP, and AP