Lavrov's comments came as he began a two-day visit to Pyongyang that is expected to lay the groundwork for a trip by President Vladimir Putin.

"We highly value your principled, unambiguous support for Russia's actions in connection with the special military operation in Ukraine," Lavrov was quoted as saying by Russia's RIA news agency.

The foreign minister's trip comes after North Korean leader Kim Jong Un travelled to Russia to meet Putin last month, his first trip abroad since the pandemic began.

Lavrov arrived in Pyongyang from Beijing, where Putin hailed Chinese President Xi Jinping on Wednesday as an "old friend" during a rare trip abroad.

Putin, guest of honour at a summit celebrating Xi's vast Belt and Road investments project, told reporters the two had met alone "eye-to-eye" and that mounting global conflicts "strengthen" their countries' relations.

Kim had travelled to Russia aboard a specially built bullet-proof train for his face-to-face meeting with Putin, declaring bilateral ties with Moscow were his country's "number one priority".

The high-profile summit fanned Western fears Pyongyang might provide Moscow with weapons for its drawn-out war in Ukraine.

On Friday, the United States said arms shipments were already under way, with North Korea delivering more than 1,000 containers of military equipment and munitions to Russia in recent weeks.

Pyongyang was seeking a range of military assistance in return, including advanced technologies, White House national security spokesman John Kirby told reporters.

- Weapons transfers -

According to a graphic provided by the White House, a load of containers was shipped by sea from North Korea to Russia between September 1 and October 1.

They were then delivered by rail to an ammunition depot about 290 kilometres (180 miles) from the Ukrainian border.

But the Kremlin said Tuesday the United States had no evidence that weapons were being shipped.

"They report this all the time, without providing any proof," Kremlin spokesman Dmitry Peskov told Russian news agencies when asked about the reported arms shipments.

Washington-based analysts Beyond Parallel last week separately released satellite images showing what they termed an "unprecedented" build-up of train traffic along Russia's border with North Korea.

The flurry of activity "likely indicates North Korea's supply of arms and munitions to Russia", the group said in its report.

While Russia has ramped up production of shells this year to a forecast 2.5 million, analysts have suggested that could fall short of its needs on the battlefield.

North Korea is a mass producer of conventional weaponry and known to be sitting on large stocks of Soviet-era war material -- albeit in unknown condition.

- Top priority -

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

The tightening of their alliance comes as relations between the two Koreas are at a historic low, with the North conducting a record-breaking series of weapons tests this year and recently enshrining its status as a nuclear state in its constitution.

South Korea has in turn moved to strengthen its security relationship with traditional ally the United States while entering a new trilateral arrangement that also includes Japan.

A US B-52 bomber capable of carrying nuclear weapons landed Tuesday at Cheongju Airport, about 100 kilometres south of Seoul, Yonhap news agency reported.

Its arrival came less than a week after the aircraft carrier USS Ronald Reagan docked in the southern port city of Busan, provoking anger from Pyongyang.

While B-52s have previously taken part in joint exercises over the peninsula, it marked the first time one has landed in the country since at least 2000, when such record-keeping began.