The European Union believes there is a "limited risk" of war in Korea, an EU official said, as the United Nations' head called the situation there "very dangerous".

"We recognise the situation as being tense and potentially volatile. But our assessment is that there is a limited risk ... of an armed conflict," the EU official said, speaking on condition of anonymity.

"We haven't seen conspicuous preparations in the North for an attack, and the situation on the ground in Pyongyang looks calm," the official said, but added that there was a risk of miscalculation or escalation that was "not negligible".

The EU will quickly adopt new sanctions onthe Democratic People's Republic of Koreapassed by the U.N. Security Council last month in response to Pyongyang's third nuclear test, the official said.

After the DPRK warned foreigners on Tuesday to evacuate South Korea to avoid being dragged into a "merciless, sacred, retaliatory war", U.N. Secretary General Ban Ki-moon expressed grave concern about the situation.

"The current level of tension is very dangerous. A small incident caused by miscalculation or misjudgement may create an uncontrollable situation," Ban told reporters in Rome.

He said he had urged the DPRK to refrain from "provocative rhetoric" and asked neighbouring countries to try to exert their influence on Pyongyang.