As Russia's invasion of Ukraine continues, a Russian newspaper has reported that former senior US national security officials have been getting in touch with high-ranking Russian presidential office members to find a way to break the deadlock. It is claimed that in some cases, US officials even visited Moscow to have face-to-face meetings. Washington denies any involvement.

The English-language newspaper The Moscow Times reported on Thursday that such talks have taken place online or by other means at least twice a month.

The paper also says former US officials have been visiting Moscow at a pace of at least every three months.

One former US official is quoted as saying the aim was to find ways of "guaranteeing Ukraine's independence while bringing Russia back as a more creative player in European security."

The former official also told the paper that if Russia thought it might lose Crimea, it would almost certainly resort to using tactical nuclear weapons.

Earlier this month the US television network NBC reported on the behind-the-scenes talks.

It said that a former assistant defense secretary was among former officials on the US side and that academics from major think tanks and others close to the Kremlin were on the Russian side.

The National Security Council's spokesperson at the White House, Adrienne Watson, tweeted on the report that the US is not seeking to open a back channel.