Instability caused by mass migration will be listed among the biggest threats to the nation, along with terrorism, radicalisation by extremist groups such as Islamic State and the potentially devastating impact of a global health scare such as ebola, The Times wrote.

The risk assessment, made every five years, will form a key element of the national security strategy, which is due to be released by the prime minister as part of a wider review of Britain's defense and security on November 23.

As UNIAN reported earlier, U.S. Army Chief of Staff Gen. Mark Milley said at the 3rd Annual Defense One Summit in Washington, DC, the United States, that he sees Russia as the number one threat to the U.S.

"I said in testimony that I considered Russia the number one threat to the United States. The reason I said that was twofold: one is capability and the second is intent. In terms of capability, Russia is the only country on Earth that has the capability to destroy the United States of America. It is an existential threat by definition, because of their nuclear capabilities. Other countries have nuclear weapons, but none as many as Russia and none has the capability to destroy – literally destroy – the United States," he said.