Officials in the Japanese city of Yokohama were left red-faced on Wednesday after mistakenly announcing the launch of a North Korean missile to 40,000 followers on Twitter.

The city, south of Tokyo, prematurely fired its Tweet just before noon (0300 GMT), announcing "North Korea has launched a missile" with blank spaces to indicate the exact time.

An official investigation into a major cyber attack on South Korean banks and broadcasters last month has determined North Korea's military intelligence agency was responsible, officials said Wednesday.

The probe into access records and the malicious codes used in the attack pointed to the North's military Reconnaissance General Bureau as the source, the Korea Internet and Security Agency (KISA) said.

South Korea raised its military watch alert to "vital threat" Wednesday before an expected North Korean missile launch, as U.N. chief Ban Ki-moon warned the Korean peninsula may be slipping out of control.

The North last week, told foreign diplomats in Pyongyang they had until April 10 to consider evacuation, fueling speculation a launch was planned between Wednesday and the April 15 birthday celebrations for late founder Kim Il-Sung.

A top U.S. military commander said Tuesday he favored shooting down a North Korean missile only if it threatened the United States or Washington's allies in the region.

When asked by lawmakers if he supported knocking out any missile fired by North Korea, Admiral Samuel Locklear, head of U.S. Pacific Command, said: "I would not recommend that."

NATO head Anders Fogh Rasmussen will visit South Korea later this week, the military alliance said Tuesday, stressing the trip was long-planned and not connected with North Korean threats of nuclear war.

Rasmussen will meet newly-elected President Park Geun-hye, Foreign Minister Yun Byung-se and Defense Minister Kim Kwan Jin on Thursday and Friday, a brief statement said.

U.N. chief Ban Ki-Moon warned Tuesday that a small incident could provoke an "uncontrollable" situation on the Korean peninsula after North Korea warned of impending "thermo-nuclear" war.

"The current level of tension is very dangerous, a small incident caused by miscalculation or misjudgment may create an uncontrollable situation," Ban said during a visit to Rome.

North Korea on Tuesday urged foreigners living in South Korea to consider evacuating, saying there was a risk of "thermo-nuclear war" breaking out on the Korean peninsula.

The warning followed a similar evacuation advisory the North gave Friday to foreign embassies in Pyongyang, saying it could not ensure the safety of their personnel if war broke out.

Japan has deployed Patriot missiles in its capital as it readies to defend the 30 million people who live in greater Tokyo from any North Korean attack, officials said Tuesday.

Two Patriot Advanced Capability-3 surface-to-air missile launchers had been stationed at the defense ministry in Tokyo before dawn, a ministry spokesman said, while Defense Minister Itsunori Onodera said "we are proceeding with measures including deployment of PAC-3 as we are on alert".

North Korean workers failed to report to work Tuesday at the joint Kaesong industrial zone with South Korea after Pyongyang suspended operations, upping the pressure on Seoul in an escalating military crisis.

"As of now, no North Korean workers have reported to work this morning," said a spokeswoman for the South's Unification Ministry.

The White House on Monday welcomed efforts by Russia and China to ease the crisis with North Korea, after pushing both nations to use their influence to change the isolated state's behavior.

"We welcome efforts by Beijing and Moscow to encourage Pyongyang to refrain from provocative rhetoric and threats," said White House spokesman Jay Carney.