North Korea has threatened to strike the South Korean capital of Seoul "without notice" over anti-Pyongyang rallies held by North Korean defectors on the anniversary of the death of former leader Kim Jong-il.
The threat to attack the capital was sent by fax from the National Defence Commission of North Korea to South Korea's National Security Council, according to Yonhap news agency.
South Korea's government responded immediately by vowing to "sternly react" to any provocation from the Communist power.
Protesters, from conservative and defection groups, rallied in Seoul and burnt photographs of the present leader of the pariah state, Kim Jong-un. North Korea called the actions the "highest indignity".
Its latest threat came against a backdrop of Dennis Rodman arriving in the country for the third time and Kim executing his own uncle, Jang Song-thaek, for "acts of treachery".
North Korea regularly threatens its neighbour. The most serious threat recently was in March when Kim moved missiles to the border with South Korea before entering a "state of war".
The outlier nation has not taken direct military action since 2010 when it launched rocket attacks on a South Korean island, killing four people.
Seoul - with a population of 10 million - lies within easy range of North Korean missiles.