North Korea has warned foreigners in South Korea to take evacuation measures in case of war.
This comes amid growing concern that the North may be about to launch a missile test.
Pyongyang has been making bellicose threats against South Korea, Japan and US bases in the region.
Japan has deployed defensive anti-missile batteries at three locations in Tokyo, to protect the capital’s 30 million residents.
US-made Patriot anti-missile systems have been deployed at the defence ministry and at two other military bases.
“The government is making utmost efforts to protect our people’s lives and ensure their safety,” Prime Minister Shinzo Abe said.
“As North Korea keeps making provocative comments, Japan, co-operating with relevant countries, will do what we have to do,” he added.
The situation on the Korean peninsula is heading for a thermo-nuclear war”
North Korean statement
At the end of last week Japan sent two of its most modern warships to the Sea of Japan with orders to shoot down any missiles fired by North Korea towards the Japanese islands.
BBC Tokyo correspondent Rupert Wingfield-Hayes say no-one in Japan thinks Pyongyang is really preparing to attack.
But it may try to fire a missile over the top of Japan in to the Pacific Ocean. If it does Tokyo has made it clear it will shoot the missile down.
This is not the first time that Japan has taken such measures.
Also on Tuesday, the South Korean news agency Yonhap reported that North Korea has completed preparations for a mid-range missile launch from its east coast
Yonhap quoted an unnamed senior military official as saying: “According to intelligence analysis of North Korea’s missile movements, it is believed to have completed preparations for a launch. Technically, it can fire off tomorrow.”
A statement attributed to Pyongyang’s Asia-Pacific Peace Committee said on Tuesday: “The situation on the Korean peninsula is heading for a thermo-nuclear war.
“In the event of war, we don’t want foreigners living in South Korea to get hurt.”
The statement urged “all foreign organisations, companies and tourists to work out measures for evacuation”.
Last Friday, Pyongyang warned it would not be able to guarantee the safety of embassy staff in the event of a war.
No foreign embassies immediately announced plans to evacuate, and the UK and Russian embassies have said they have no immediate plans to shut their embassies.
The United States, which has also been threatened by Pyongyang, has said there were no imminent signs of threats to American citizens.
The UK Foreign and Commonwealth advice on travel to South Korea was that there was “no immediate increased risk or danger to those living in or travelling to South Korea” as a result of the North Korean warning last Friday.
Tuesday’s warning to foreigners in South Korea is the latest step in the escalation of tension on the Korean peninsula.
North Korean employees on Tuesday did not report for work at the Kaesong Industrial Complex, suspending one of the few points of co-operation between North and South Korea.
The United Nations imposed tough sanctions on North Korea last month following its third nuclear test.
Pyongyang has responded to this and to joint military exercises between South Korea and the US with escalating rhetoric. It has threatened to use nuclear weapons and said it would restart a nuclear reactor.
The North has also shut down an emergency military hotline between Seoul and Pyongyang.