In recent months, US National Security Adviser Jake Sullivan has engaged in confidential conversations with top aides to Russian President Vladimir Putin to reduce the risk of a broader conflict over Ukraine and to warn Moscow against the use of nuclear or other weapons of mass destruction, according to US and allied officials speaking to The Wall Street Journal on Sunday.

According to the officials, Sullivan has been in communication with Yuri Ushakov, Putin's foreign policy adviser. The authorities noted that Sullivan has also spoken with his direct counterpart in the Russian government, Nikolai Patrushev.

The sources told The Wall Street Journal that the goal was to guard against the potential of escalation and maintain communication channels, not to negotiate a resolution to the crisis in Ukraine.

When asked if Sullivan had secret communications with Ushakov or Patrushev, National Security Council spokesperson Adrienne Watson responded, "People say a lot of things" and declined to comment more. The Kremlin declined to react in response to a request.

Putin offered a barely veiled threat to deploy nuclear weapons in a recent address, during which he also declared Russia's first wartime military mobilization since World War II.

In his address to the United Nations General Assembly, President Joe Biden accused Vladimir Putin of making "overt nuclear threats to Europe" in reckless contempt for nuclear nonproliferation obligations.

Later, Sullivan stated that Washington takes Putin's nuclear threats seriously but currently sees no indicators of a Russian nuclear strike.