SEOUL (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.

"North Korea should refrain from all provocative actions, including missile launches, which are in clear violation of U.N. resolutions," Sung Kim, the U.S. special envoy for North Korea, told reporters in Seoul when asked about Monday's firing.