WASHINGTON -- North Korea has delivered more than 1,000 containers of military equipment and munitions to Russia in recent weeks for use in Ukraine, a White House official said Friday, lambasting burgeoning cooperation between Pyongyang and Moscow as a threat to regional stability.

In a press briefing, John Kirby, National Security Council coordinator for strategic communications, disclosed the information, amid persistent speculation that the Sept. 13 summit between North Korean leader Kim Jong-un and Russian President Vladimir Putin might have led to an arms deal.

Kirby also voiced concerns about possible Russian assistance to the North in return for arms support, disclosing the US' observation that Russian ships offloaded containers in the North, which he said "may constitute the initial deliveries of material from Russia."

"Our information indicates that in recent weeks, North Korea has provided Russia with more than 1,000 containers of military equipment and munitions," he said.

The White House released imagery showing that between Sept. 7 and Oct. 1, a set of containers were shipped from Najin, North Korea, to Dunay, Russia, via MV Angara, a Russian-flagged cargo ship. The shipping containers were then moved via rail to an ammunition depot in southwestern Russia near Tikhoretsk, roughly 290 kilometers from the Ukrainian border.

One of the photos also showed a shipment of about 300 shipping containers at Najin for delivery to Russia on Sept. 7-8 -- an indication that a decision on such an arms transfer was made prior to the rare meeting between Kim and Putin at the Vostochny Cosmodrome, a Russian spaceport.

"We condemn the DPRK for providing Russia with this military equipment, which can be used to attack Ukrainian cities and kill Ukrainian civilians, and for the Russians and illegitimate war," Kirby said, referring to North Korea by its official name, the Democratic People's Republic of Korea.

The official also raised the possibility that Russia could offer something in exchange.

"We also are increasingly concerned about Russian assistance to the DPRK," he said. "In return for support, we assess that Pyongyang is seeking military assistance from Russia, including fighter aircraft, surface-to air missiles, armored vehicles, ballistic missile production equipment, or other materials and other advanced technologies."

He stressed that the US is "closely" monitoring whether Russia will offer such military assistance to the North.

"We have already observed Russian ships offloading containers in the DPRK, which may constitute the initial deliveries of material from Russia," he said. "This expanding military partnership between the DPRK and Russia, including any technology transfers from Russia to the DPRK undermines the regional stability and the global Non-proliferation regime.

In response to the expanding military ties between the North and Russia, the US will take a range of steps that include pursuing new sanctions against those seeking to enable arms deals between the two countries, and "aggressively" raising the issue at the United Nations Security Council (UNSC), according to Kirby.

Seoul and Washington have said that any arms transfers between Pyongyang and Moscow would be in violation of UNSC resolutions that Russia itself voted for.

The disclosure of information on the arms trade between the North and Russia appears intended to prevent the two countries from engaging in additional arms transactions and warn other countries not to provide arms support to Russia, observers said.

In Beijing this month, Chinese President Xi Jinping and Putin are expected to meet on the margins of the Belt and Road Initiative Forum, a massive China-led global infrastructure and energy project, raising questions over whether Putin would seek military support from Xi. The conference on Oct. 17-18 marks the 10th anniversary of the project.

The disclosure also came amid lingering speculation that Iran and North Korea could play a role in replenishing the weapons inventory of the Hamas militant group whose surprise attack last week sparked its escalating conflict with Israel.

During a UNSC session at the UN headquarters in New York, John Kelley, political minister counselor at the United States Permanent Mission at the UN, called on the North to stop its arms transfers to Russia.

He cited a recent analysis of satellite imagery showing a "dramatic" surge in rail traffic along the border between North Korea and Russia. The analysis was done by Beyond Parallel, a project of the Washington-based Center for Strategic and International Studies.

"We again urge the DPRK to cease its efforts to transfer arms to Russia," he said. "We again call on Russia to recommit to the maintenance of peace and security and its obligations to uphold the UN arms embargo on the DPRK that Russia itself voted to adopt." (Yonhap)