Putin's spy chief tells U.S: Ukraine will become your Vietnam

Putin sent troops into Ukraine early last year, triggering a war that has killed or wounded hundreds of thousands and led to the biggest confrontation between Russia and the West in six decades.

The West has given Ukraine more than $246 billion in aid and weapons, but a Ukrainian counteroffensive has failed and Russia remains in control of just under a fifth of Ukrainian territory.

"Ukraine will turn into a 'black hole' absorbing more and more resources and people," Sergei Naryshkin, head of Russia's Foreign Intelligence Service (SVR), said in an article in the SVR's house journal, "The Intelligence Operative".

"Ultimately, the U.S. risks creating a 'second Vietnam' for itself, and every new American administration will have to try to deal with it."

U.S. President Joe Biden has warned that a direct NATO-Russia confrontation could trigger World War Three and repeatedly ruled out sending American soldiers to Ukraine.

The Vietnam War was in effect an East-West Cold War conflict in which the United States fought alongside the forces of South Vietnam against a north supported by the communist powers of China and the Soviet Union.

The war, in which several million were killed, ended in 1975 with victory for North Vietnam and ignominious defeat for the United States, which had lost more than 58,000 of its own combatants and kindled a powerful anti-war movement at home.

Biden pleaded with Republicans on Wednesday for a fresh infusion of military aid for Ukraine.

"If Putin takes Ukraine, he won’t stop there," Biden said, predicting that Putin would go on to attack a NATO ally.

Then, Biden added, "we’ll have something that we don't seek and that we don't have today: American troops fighting Russian troops".