KCNA picture shows North Korean leader Kim Jong Un watching landing and anti-landing exercises being carried out by the Korean People's Army at an unknown location Thomson Reuters

North Korea fired five short-range projectiles into the sea off its east coast on Monday, South Korea's military said, amid heightened tension over the isolated country's nuclear and rocket programs.

The unidentified projectiles were launched from south of the city of Hamhung and flew about 200 km (120 miles), landing in waters east of North Korea, South Korea's Joint Chiefs of Staff said in a statement.

On Friday, North Korea fired two mid-range ballistic missiles into the sea in defiance of tough new U.N. and U.S. sanctions slapped on the country following nuclear and rocket tests earlier this year.

In recent weeks, North Korea has stepped up its bellicose rhetoric, threatening pre-emptive nuclear strikes against Washington and Seoul and firing short-range missiles and artillery into the sea.

The North protests annual ongoing joint U.S.-South Korea military drills.

North Korean leader Kim Jong Un said last week that the country would soon test a nuclear warhead and ballistic missiles capable of carrying nuclear warheads in what would be a direct violation of U.N. resolutions that have the backing of Pyongyang's chief ally, China.