Senior US administration officials said the White House has formed a team of experts to come up with plans for a possible US response if Russia uses chemical, biological or nuclear weapons of mass destruction in Ukraine, according to Reuters.

The Kremlin said this week that such weapons would only be used in the case of an "existential threat".

But US officials have warned that Russia's accusations that Ukraine may use chemical weapons is a lie that may indicate that Moscow may resort to using them, given similar precedents.

The officials said the White House National Security Council sent an internal memo to security agencies and agencies dated February 28 requesting the formation of a strategic group to examine the major geopolitical shifts that are occurring as a result of Russia's "invasion of Ukraine."

Another team, known internally as the "Tiger Team", is looking into potential forecasts for the next three months.

One of the officials said the strategy group was working "to monitor and mitigate risks while looking at how to advance and defend US interests."

The official added that this team is developing contingency plans for various scenarios and possibilities, including the possibility of Russia resorting to the use of chemical or biological weapons, targeting American security convoys, disrupting global food supply chains, and the ongoing response to the escalating refugee crisis.

The official noted that the team is also looking into the possibility of Russia's use of nuclear weapons.

The official declined to speculate on the US response to Russia's possible use of weapons of mass destruction, saying there would be a response.

In this context, the leaders of the Group of Seven major industrialized countries warned Russia on Thursday - in a statement after talks in Brussels - of the consequences of using biological, chemical or nuclear weapons in its war on Ukraine.

"We warn against any threat of use of chemical, biological or nuclear weapons or any related materials," the leaders said in a joint statement published by Germany.