(AFP) North Korea and Russia signed a mutual defense agreement Wednesday during a visit to Pyongyang by Vladimir Putin, who thanked the leader of the enigmatic communist country, Kim Jong Un, for supporting Russia's military offensive against Ukraine.

During the official visit, the North Korean leader met Putin on the tarmac of the airport. The streets of Pyongyang were decorated with portraits of the Russian leader On Thursday he will continue his tour and visit Vietnam, Moscow's partner since Soviet times.

"The comprehensive partnership treaty signed today provides, among other things, for mutual assistance in case of aggression against one party," Putin said after signing the document.

Russia "does not rule out" military-technical cooperation with North Korea, said the leader, who is the subject of an arrest warrant issued by the International Criminal Court.

"Today, we are fighting together against the hegemonic and neo-colonialist practices of the United States and its satellites," he added, as quoted by Russian media, during a gala party in his honor.

According to the North Korean leader, the treaty will "reliably guarantee the alliance" between the two countries and contribute "fully to the maintenance of peace and stability in the region".

Western powers, which for months have accused North Korea of supplying Russia with munitions and missiles for the war in Ukraine, fear a strengthening of military cooperation between Moscow and Pyongyang.

Ukrainian presidential adviser Mikhail Podoliak accused Pyongyang of helping Russia militarily and demanded stronger measures to isolate both countries.

"North Korea today actively cooperates with Russia in the military sphere and deliberately provides it with resources for the mass murder of Ukrainians," he criticized.

North Korea's "full support"

Putin reiterated that "Russia and Korea carry out their own independent foreign policy, and do not accept the language of blackmail", and Kim welcomed a "new era" of bilateral relations.

"North Korea expresses its full support and solidarity with the government" in its offensive in Ukraine, the North Korean leader stressed, implying a critique of the sanctions against Moscow.

Kim Jong Un stressed that the mutual assistance agreement is "defensive" in nature, according to Russian press agencies, and called Putin North Korea's "best friend".

Putin thanked Kim for North Korea's "constant and unwavering" support, invited him to visit Moscow and advocated that sanctions against Pyongyang be "reviewed".

Moscow and Pyongyang have been allies since the end of the Korean War (1950-1953) and have had closer relations since the beginning of Russia's invasion of Ukraine in February 2022.

Putin was greeted with great fanfare in Pyongyang's Kim Il Sung Square with a military band and a synchronized dance performance, which are customary for ceremonies in North Korea.

The leaders then began a meeting, their second meeting in less than a year after Kim visited Russia in September. Putin's previous visit to the inscrutable communist country dates back to 2000.

A U.S. State Department spokesman told AFP that "deepening cooperation between" the two countries "should be of concern to anyone interested in maintaining peace and stability on the Korean peninsula".

For Koh Yu-hwan, professor emeritus of North Korean studies at Dongguk University in Seoul, "Russia needs North Korea's support in armaments because of the protracted war in Ukraine, while North Korea needs Russia's support in food, energy and cutting-edge weapons to ease pressure from sanctions."

U.S. expresses "concern"

Pyongyang dismissed accusations that it supplies weapons to Russia as "absurd."

Russia used its veto power in the UN Security Council in March to end the system for monitoring sanctions against North Korea, which were imposed mainly because of Pyongyang's nuclear program.

The Russian leader traveled with Foreign Minister Sergey Lavrov and Defence Minister Andrei Belousov.

Putin, who is the subject of an International Criminal Court arrest warrant, has scaled back his foreign travel but has made some trips to visit key allies such as China.

Putin's support allows Kim to "balance his dependence" on his other key ally China, Vladimir Tikhonov, an academic at the University of Oslo, told AFP. In return "he gets a secure supply of the Soviet-style artillery shells he needs."