How Russia and US will come to the table

Vladimir Frolov, who analyzes Russian politics, said that in diplomatic parlance such behavior is known as "demarche"－a demonstration of strong dissatisfaction with a political partner's actions and statements, but without any concrete negative consequences－yet.

The key question is whether Biden's unexpectedly harsh statement about Putin was simply another example of his well-known "linguistic intemperance", or a calculated and deliberate escalation of his personal conflict with the Russian leader－a direct challenge that the Kremlin could not ignore, Frolov said.

Shortly after the "killer" remarks, former Russian president and prime minister Dmitry Medvedev warned that relations between Moscow and Washington had plummeted to levels last seen during the Cold War.

"In recent years, relations between Russia and the United States have actually shifted from rivalry to confrontation, essentially returning to the Cold War era," said Medvedev, who now serves as deputy chairman of his country's Security Council.

"Sanctions pressure, threats, confrontation, defense of one's selfish interests－all of this is plunging the world into a state of permanent instability," he added.

As Kremlin spokesman Dmitry Peskov said, US-Russian relations are more fraught than ever, and have now hit the bottom.

Robert Legvold, director of the Euro-Atlantic Security Initiative, said Biden's undiplomatic language may have triggered greater indignation than previous US rhetoric. The sanctions may have stung a little more, coming a day after the two presidents held a constructive conversation, but they fall within a pattern of discord that has characterized the relationship for the past seven years, he said.

"The question is whether the advent of the Biden administration will lead to a further hardening of US policy and a tit-for-tat Russian response or, alternatively, create an opening for the two sides to try tentatively to move relations in a more constructive direction," he said.