South Korea's Yonhap news agency says North Korea has fired 100 artillery shells into the sea.

Yonhap said Monday that the shells fired from multiple rocket launch systems into waters north of the eastern sea border between the countries. It gave no further details.

Repeated calls to South Korea's Defense Ministry and Joint Chiefs of Staff were not immediately answered.

The reported firing came a day after North Korea test-launched two ballistic missiles into waters off its east coast in the latest in a series of weapons tests the country has been conducting.