"We believe that the DPRK [Democratic People's Republic of Korea] has sent around 10,000 soldiers in total to train in eastern Russia," Deputy Pentagon press secretary Sabrina Singh said.

American agencies have assessed that China dislikes the growing partnership between Russia and North Korea. The State Department has raised the troop issue with Chinese diplomats.

President Vladimir Putin suggested on Thursday that Russia could hold military drills with North Korea. "We'll see. We could also conduct exercises. Why not?," Putin said, when asked whether Moscow would conduct joint military drills with Pyongyang.