The North Korean government has announced plans to "liquidate" all remaining South Korean assets at former joint projects in its territory in response to sanctions imposed by Seoul.

The move came amid an escalating standoff that began in January between the two sides.

The North's Committee for the Peaceful Reunification of Korea said in a statement on Thursday that Pyongyang will seize its neighbour's assets at the closed Kaesong industrial complex and the scrapped tourism resort at Diamond Mountain.

It said it will also take a series of unspecified steps to impose "lethal" military, political and economic blows on the South Korean government to accelerate what Pyongyang called its "pitiable demise".

In another show of defiance on Thursday, North Korea also fired short-range ballistic missiles that fell into waters off South Korea's east coast, according to the South Korean defence ministry. They are believed to be Scud-type missiles, said ministry spokesman Moon Sang-gyun.

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Such missile firings by the North are not uncommon as a way of protesting annual military drills carried out by Seoul and Washington. The drills, which this year are described as the biggest ever, are expected to take place this month.

Pyongyang is also angry over tough United Nations sanctions following its recent nuclear test and long-range rocket launch.

Nuclear warhead model

The latest firings come a day after North Korea caused a new stir by publicising a purported mock-up of a key part of a nuclear warhead, with leader Kim Jong-un repeating a claim that his country has developed miniaturised atomic bombs that can be placed on missiles.

READ MORE: North Korea threatens nuclear strike

The moves are the latest in an increasing standoff between the Koreas that began in January when North Korea detonated what it said was an "H-bomb of justice," its fourth nuclear test.

Since then, Seoul has shut down the last remaining cooperative project between the rivals, a jointly run factory park in the North Korean border town of Kaesong, and slapped sanctions on the North over its recent nuclear test and rocket launch.

The UN has imposed sanctions, and the North has threatened nuclear strikes on Seoul and the US mainland.

The North's statement called South Korea's unilateral sanctions "laughable, unsightly" behaviour, and referred to South Korea's female president, Park Geun-hye, as an "American prostitute," the latest in a series of crude derogatory attacks on her.

Source: Agencies