The trip is Putin's first to the isolated nation in 24 years.
Russian President Vladimir Putin landed in North Korea early Wednesday, the Kremlin said, kicking off a visit set to boost defence ties between the two nuclear-armed countries as Moscow pursues its war in Ukraine.
Just after the pre-dawn touchdown, Russian TV showed North Korean leader Kim Jong Un greeting Putin in the dark, on a red carpet at Pyongyang's airport, with the pair shaking hands and embracing before a motorcade took Putin along streets lined with Russian flags.
The trip is Putin's first to the isolated nation in 24 years, with a recent confrontation between North and South Korean troops on the countries' shared border highlighting regional security tensions.
Moscow and Pyongyang have been allies since North Korea's founding after World War II and have drawn even closer since Russia's invasion of Ukraine in 2022 led to the West isolating Putin internationally.
The United States and its allies have accused North Korea of supplying Russia with much-needed arms, including ballistic missiles to use in Ukraine.
The North has denied giving Russia military hardware, but ahead of his trip, Putin thanked Kim's government for helping the war effort.
"We highly appreciate that the DPRK (North Korea) is firmly supporting the special military operations of Russia being conducted in Ukraine," Putin wrote in an article published by Pyongyang's state media Tuesday.
Russia and the North are "now actively developing the many-sided partnership", Putin wrote.
Both countries are under rafts of United Nations sanctions -- Pyongyang since 2006 over banned nuclear and ballistic missile programmes and Moscow over the invasion of Ukraine.
Putin praised North Korea for "defending their interests very effectively despite the US economic pressure, provocation, blackmail and military threats that have lasted for decades".
He also hailed Moscow and Pyongyang for "maintaining the common line and stand at the UN".
North Korea said the visit showed bilateral ties "are getting stronger day by day", the official Korean Central News Agency reported.
- US concern -
Pyongyang has described allegations of supplying weapons to Russia as "absurd".
However, it did thank Russia for using its UN veto in March to effectively end monitoring of sanctions violations just as UN experts were starting to probe alleged arms transfers.
The United States voiced "concern" Monday about Putin's trip because of the security implications for South Korea as well as Ukraine.
The two Koreas have remained technically at war since their 1950-53 conflict and the border dividing them is one of the most heavily fortified in the world.
"We know North Korean ballistic missiles are still being used to hit Ukrainian targets (and) there could be some reciprocity here that could affect security on the Korean peninsula," National Security Council spokesman John Kirby told reporters.
Highlighting those security concerns, South Korea said its troops fired warning shots at soldiers from the North who briefly crossed the border Tuesday and then retreated.
The South's military said it believed the North Korean soldiers accidentally crossed as they were fortifying the border, but said some of them were wounded after detonating landmines.
- 'Lonely bromance' -
NATO Secretary General Jens Stoltenberg said Putin's trip showed how he was "dependent" on authoritarian leaders.
"Their closest friends and the biggest supporters of the Russian war effort -- war of aggression -- (are) North Korea, Iran and China," Stoltenberg said.
Ukraine's Foreign Minister Dmytro Kuleba urged the international community to counter "the lonely bromance" between Putin and Kim by increasing arms supplies to Kyiv.
"The best way to respond to it is to continue strengthening the diplomatic coalition for just and lasting peace in Ukraine and delivering more Patriots and ammunition to Ukraine," Kuleba told AFP.
North Korea is eager for high-end military technology to advance its nuclear, missile, satellite and nuclear-powered submarine programmes, according to experts.
The Kremlin released a document on Tuesday confirming that Russia plans to sign a "strategic partnership" treaty with North Korea.
Given North Korea's chronic resource shortages, Pyongyang is expected to discuss ways to strengthen cooperation in areas such as tourism, agriculture and mining, "in exchange for providing military supplies" to Russia, a report from the Seoul-based Institute for National Security Strategy said.
Other issues including "cooperation on the deployment of North Korean workers or the supply of energy to North Korea -- both of which would violate sanctions... are also likely to be discussed" behind the scenes, INSS researcher Kim Sung-bae wrote.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)