Following Biden's statement that implied otherwise, the White House said it has "no intention" of employing prohibited narcotics. The US has no intention of using chemical weapons under any circumstances," according to National Security Advisor Jake Sullivan, who spoke to reporters on Friday.

The comment comes after President Joe Biden said on Thursday that a Russian deployment of such substances in Ukraine would trigger “a response in kind.”

Sullivan told reporters onboard Air Force One on Friday that Biden's use of the phrase "respond in kind" referred to proportionality and that "there will be a high price if Russia deploys chemical weapons."

Biden refuses to rule out territorial concessions by Ukraine. Biden, UK Prime Minister Boris Johnson, and NATO Secretary-General Jens Stoltenberg have all warned Russia that such an action would be greeted with a serious retaliation, though none have specified what that retaliation might be and without offering any proof of Russia's intention to use such weapons.

Washington and its allies have accused Moscow of preparing to deploy chemical weapons in Ukraine, but Russia has denied the claims and suggested that Kiev may be organizing a "false flag" strike to put on Russia to elicit NATO intervention.

Meanwhile, Russia has released documents purporting to demonstrate that the United States was sponsoring biological weapons research in many Ukrainian institutions. American authorities have called Moscow's claims "disinformation", even though they have acknowledged the existence of the facilities, and the US administration has admitted to working with Ukraine to "consolidate and safeguard diseases and poisons of security importance."

Following a seven-year deadlock over Kiev's inability to fulfill the provisions of the Minsk agreements and end the conflict with the separatist regions of Donetsk and Lugansk, Russia moved soldiers into Ukraine in late February. Russia eventually recognized the two as separate entities, at which point they requested military assistance.

Russia insists that Ukraine publicly declare itself a neutral country that will never join the NATO military alliance led by the United States. Kiev claims that the Russian operation was utterly unprovoked and refutes assertions that it intended to seize the two Donbass republics by force.