Vladimir Putin has been dealt a blow by two of his closest allies who have failed to endorse the sending of North Korean troops to fight for Russian forces against Ukraine. Experts are also casting doubt on the strategic worth of such a move by the Russian leader.

President Vladimir Putin, asked about reports that North Korea had sent thousands of troops to Russia, said on Thursday that it was Moscow's business how to implement a partnership treaty with Pyongyang.

Russian lawmakers have ratified a pact with North Korea envisioning mutual military assistance, a move that comes even as the U.S. confirmed the deployment of 3,000 North Korean troops to Russia.