Historical allies Russia and North Korea are both under a raft of global sanctions -- Moscow for its invasion of Ukraine and Pyongyang for its testing of nuclear weapons.

Their leaders Vladimir Putin and Kim Jong Un held a summit in Russia's far east in September, with the United States subsequently claiming Pyongyang had begun providing Moscow with weapons.

"The number of containers from the North to Russia has increased by 300 to reach around 7,000 containers in total so far," Defence Minister Shin Won-sik said at a media briefing Monday, his ministry told AFP.

The figure refers to shipments sent since July and Shin said that with "some maritime routes suspended now, some have been sent via rail to Russia".

The United States said in October 2023 that arms shipments from Pyongyang to Moscow were underway, estimating that North Korea had delivered more than 1,000 containers of military equipment and munitions to Russia at the time.

Seoul accused Pyongyang the following month of sending more than one million artillery rounds to Russia, with the North appearing in return to receive technical advice from Moscow on its bid to launch a military reconnaissance satellite.

Kim declared during his visit to Russia in September that bilateral ties with Moscow were his country's "number one priority", with Pyongyang becoming an ardent supporter of Moscow's invasion of Ukraine.

Washington and experts have said Pyongyang was seeking a range of military assistance in return, such as satellite technology and upgrading its Soviet-era military equipment.

North Korea's state media said on Monday Kim had sent a message congratulating Russian President Vladimir Putin on his landslide re-election for a fifth term in office.

"I will firmly join hands with you and bring about a new era of the DPRK-Russia friendship," the message said.