North Korea's Korean Central News Agency released a photo of their submarine-launched ballistic missile Pukkuksong-3 in this Oct. 3, 2019 file photo. Yonhap

South Korea will strengthen sanctions against North Korea in cooperation with such other countries as the United States and Japan if Pyongyang carries out another nuclear test or other grave provocations, Seoul's foreign ministry said Monday.

In a report submitted to the National Assembly's foreign affairs and unification committee, the ministry pointed out the level of North Korea's missile provocations this year has been more serious than ever.

The North is exploiting the worsening of Washington's relations with Beijing and Moscow, which has caused difficulties of the U.N. Security Council members standing united against Pyongyang's provocations, it added.

Last week, Seoul slapped new sanctions on eight individual and seven institutions related to the North's missile program, while Washington newly added three senior members of the country's ruling party to its blacklist. Tokyo also imposed its own sanctions on three North Korean institutions and one individual.

Speaking at the committee's session, Unification Minister Kwon Young-se said a North Korean nuclear test may not be imminent, but the country appears to feel the need for testing to develop lighter and smaller nuclear warheads for tactical weapons.

On the possibility that North Korea may skip a nuclear test this year, the minister said, "I think so for now, but it is hard to predict (the timing)."

In regard to North Korean leader Kim Jong-un appearing with his daughter at the scene of last month's missile test, Kwon said "It is too early to say (that the move is related to) a hereditary succession."

North Korea revealed Kim Jong-un's daughter, presumed to be his second daughter Ju-ae, for the first time last month in photos showing them attending the test-firing of what appears to be a Hwasong-17 intercontinental ballistic missile (ICBM) on Nov. 18. (Yonhap)