U.N. Secretary-General Antonio Guterres is "deeply concerned" that North Korea has indicated it could resume nuclear and missile tests, a U.N. spokesman said on Wednesday.

"The Secretary-General very much hopes that the tests will not resume, in line with relevant Security Council resolutions. Non-proliferation remains a fundamental pillar of global nuclear security and must be preserved," spokesman Stephane Dujarric said in a statement.

North Korean leader Kim Jong Un said this week that there were no longer grounds for Pyongyang to be bound by a self-declared moratorium on intercontinental ballistic missile and nuclear bomb testing and that a "new strategic weapon" would be introduced in the near future.