Russian President Vladimir Putin signed into law a treaty on the country’s strategic partnership with North Korea, which includes a mutual defense provision, according to a decree published on Saturday.

The accord, signed by Putin and North Korean leader Kim Jong Un in June after a summit in Pyongyang, calls on each side to come to the other’s aid in case of an armed attack.

Russia’s upper house ratified the treaty this week, while the lower house endorsed it last month. Putin signed a decree on that ratification that appeared on Saturday on a government website outlining legislative procedures.

The treaty galvanizes closer ties between Moscow and Pyongyang since Russia launched its full-scale invasion of Ukraine in February 2022.

Reports from South Korea and Western countries say North Korea has supplied Russia with weaponry. Ukrainian forensic experts say they have found traces of the weapons at sites of Russian attacks.

Ukrainian President Volodymyr Zelenskiy said on Thursday that North Korea has sent 11,000 troops to Russia and some of them suffered casualties in combat with Kyiv’s forces in Russia’s southern Kursk region.

Russia has not confirmed the presence of the North Korean troops.