SEOUL, South Korea (AP) — North Korea ratified a major defense treaty with Russia stipulating mutual military aid, the North’s state media reported Tuesday, as the U.S., South Korea and Ukraine say North Korea has sent thousands of troops to Russia to support its war against Ukraine.

Russia had completed the ratification of the treaty last week after it was signed by Russian President Vladimir Putin and North Korean leader Kim Jong Un in June. It is considered both countries’ biggest defense deal since the end of the Cold War.

The Comprehensive Strategic Partnership treaty will take effect when both sides exchange documents on the ratification, the state-run Korean Central News Agency said.

North Korea ratified the treaty through a decree signed Monday by the country's president of state affairs, KCNA said, using one of Kim's titles.

North Korea’s rubber-stamp parliament, the Supreme People’s Assembly, has the right to ratify treaties but Kim can unilaterally ratify major ones, according to South Korea’s Unification Ministry.

The treaty requires both countries to use all available means to provide immediate military assistance if either is attacked. Some observers speculate the treaty’s ratification in both countries could signal North Korea could formally enter the Russia-Ukraine war soon.

According to U.S., South Korean and Ukrainian intelligence assessments, up to 12,000 North Korean troops have been sent to Russia likely as part of the June treaty. Last week, Ukrainian officials said Ukraine and North Korean troops engaged in small-scale fighting while Ukraine’s army fired artillery at North Korean soldiers in Russia’s Kursk border region.

North Korea’s troop dispatch threatens to escalate the almost three-year war. South Korea, the U.S. and their partners also worry about what Russia could give North Korea in return. Possible Russian transfer of sensitive technology to enhance North Korea’s already-advancing nuclear and missile programs would be an alarming development for the U.S. and its allies.

North Korea and Russia have been significantly strengthening their military and other cooperation. South Korea’s spy agency said last month that North Korea had sent more than 13,000 containers of artillery, missiles and other conventional arms to Russia since August 2023 to replenish its dwindling weapons stockpiles.