North Korea says leader Kim Jong Un has signed a decree to ratify a bilateral treaty with Russia, which calls for mutual military assistance if either country is attacked.

Tuesday's edition of North Korea's ruling Workers' Party newspaper, Rodong Sinmun, said Kim signed the ratification decree for the comprehensive strategic partnership treaty on Monday.

Kim and Russian President Vladimir Putin signed the treaty in June when Putin visited Pyongyang. Russia ratified the accord on Saturday.

The North Korean report says the treaty will take effect from the day when both sides exchange their ratification instruments.

The treaty stipulates that if either of the parties is invaded and placed under a state of war, the other will deploy all means in its possession to provide military and other assistance, without delay.

South Korea's Yonhap News Agency says North Korea and Russia are effectively forming a military alliance. North Korea has sent troops to Russia, as its invasion of Ukraine continues.