North Korea has fired two short-range ballistic missiles into the sea, South Korea's military has said, according to BBC News.

It said the missiles, launched off the east coast, flew some 500km (310 miles) and fell into the water.

Shortly after the launch, Pyongyang announced it "nullifies" all inter-Korean cooperative projects and will liquidate South Korean assets in the country.

Most South Korean assets in the North are in the Kaesong industrial zone.

South Korea pulled out of the jointly-operated industrial zone in February, after North Korea's latest long-range missile launch of a satellite. At the time, the North called the shutdown "a declaration of war" and designated Kaesong as a military zone.

On Wednesday, March 10 North Korean leader Kim Jong-un also claimed scientists had developed nuclear warheads small enough to fit on ballistic missiles.

However, South Korea's defence ministry said it thought the North had "not yet secured miniaturised nuclear warheads".

The claim is critical, as without miniaturisation Pyongyang cannot put its nuclear weapons on missiles - an ability many analysts think could still be several years away.