Speaking in New York, Mr. Sullivan declared that being in touch with the Kremlin was “in the interests” of the United States.
He emphasised, though, that the authorities were “clear-eyed about who we are dealing with.”
It happens at a time when the White House won’t confirm or deny claims that Mr. Sullivan has been in charge of negotiations with Russia to avoid a nuclear crisis in Ukraine.
The Security Council secretary for Russia, Nikolai Patrushev, and top Kremlin foreign policy advisor Yuri Ushakov, according to reports, have had private conversations with Mr. Sullivan during the past few months.
Senior authorities told the newspaper that although the men hadn’t participated in any conversations about how to end the fight, they had discussed how to prevent the possibility of nuclear escalation in the Ukraine war.
The use of nuclear weapons would have “catastrophic consequences for Russia,” according to Mr. Sullivan’s statement from last month. He claimed to the US network that senior government officials had “spelled out” to Russian officials in private conversations the extent of a potential US retaliation.
Adrienne Watson, a spokeswoman for the US National Security Council, declined to corroborate the report, telling the newspaper that “people claim a lot of things,” while Dmitry Peskov, a spokesman for the Kremlin, charged that Western media outlets had “published numerous hoaxes.”
However, according to Karin Jean-Pierre, the press secretary for the White House, the US has reserved the authority to undertake negotiations with Russia.
And Mr. Sullivan, who is reportedly one of US President Joe Biden’s most senior advisers and is still pressing for talks with Russia, claimed that keeping in touch with Moscow was in the “interests of every country who is affected by this conflict.”
The sources reported last week that senior US officials were pressuring Kyiv to show it was willing to engage in talks with Russia and withdraw its outspoken objection to doing so while President Vladimir Putin was still in office.
At a public speech in New York, Mr. Sullivan asserted that the Biden government had “an obligation to pursue accountability” and made a commitment to collaborate with other nations to “hold the perpetrators of grave and grotesque war crimes in Ukraine responsible for what they have done.”
“I was just in Kyiv on Friday. and I had the opportunity to meet with President [Volodymyr] Zelensky and my counterpart Andriy Yermak, with the military leadership and also to get a briefing on just what level of death and devastation has been erupted by Putin’s war on that country,” Mr. Sullivan added.
The possibility that Russia would use nuclear weapons in a desperate effort to protect four regions of eastern and southern Ukraine that it illegitimately annexed has become more frightening in recent months.
While everything was going on, Ukraine used its armed conflict martial laws to seize five crucial businesses’ assets.
Some of the enterprises have ties to the imprisoned tycoon Vyacheslav Bohuslayev, who is suspected of working with Russia. These include two energy companies, as well as businesses that produce engines, automobiles, and transformers.
According to President Zelensky, the action would assist Ukraine’s defence industry in meeting the demands of the military, which is presently engaged in counteroffensives in the country’s south and east.