MOSCOW (AP) — Russian lawmakers on Thursday ratified a pact with North Korea envisioning mutual military assistance, a move that comes as the U.S. confirmed the deployment of 3,000 North Korean troops to Russia.

The lower house of the Russian parliament, the State Duma, voted quickly to endorse the “comprehensive strategic partnership” treaty that Russia's President Vladimir Putin signed with North Korean leader King Jong Un on a visit to Pyongyang in June. The upper house is expected to follow suit soon.

The pact obliges Russia and North Korea to immediately provide military assistance using “all means” if either is attacked. It marked the strongest link between Moscow and Pyongyang since the end of the Cold War.

The U.S. said Wednesday that 3,000 North Korean troops have been deployed to Russia and are training at several locations, calling the move very serious and warning that those forces will be “fair game” if they go into combat in Ukraine.

Asked at a news conference during the BRICS summit in Kazan, Russia, whether North Korean troops were inside his country, Putin noted the lawmakers’ ratification of the “strategic partnership” with Pyongyang.

“We have never doubted that the North Korean leadership takes our agreements seriously. What and how we will do within the framework of this article (of the agreement) is our business,” he said.

Russia and North Korea have previously rejected assertions by the U.S. and its allies that Pyongyang has given Moscow ballistic missiles and millions of artillery shells for use in Ukraine.

Asked in June whether North Korean troops could fight alongside Russian forces in Ukraine under the pact, Putin said there was no need for that but he also announced for the first time that Russia could provide weapons to Pyongyang.

Observers said that in exchange for military support Moscow could share sophisticated weapons technologies with Pyongyang to help improve its ballistic missile and satellite capabilities.