Biden admin avoiding 'red line' over any Russian use of chemical weapons in Ukraine

The Biden administration official is steering clear of defining any use by Russia of chemical weapons in Ukraine as a "red line," a senior administration official told ABC News.

"We learned our lesson" the official said in describing the Obama administration's ineffective response to Syria's use of chemical weapons in 2012.

Instead, the administration is considering a new round of economic sanctions against Russia as a potential response should Russia use chemical or biological weapons in Ukraine, according to a senior administration official.

A senior administration official told ABC News that the U.S. would most likely respond to Russia's use of chemical and biological weapons "with dramatically stepped-up" sanctions that could target Russia's gold reserves or Russian leadership.

However, the official noted that developing additional rounds of sanctions might be difficult to put into play given the wide range of international sanctions against Russia that have been put in place since Russia's invasion.

ABC News has previously reported that the Biden administration and NATO are looking to get chemical and biological detection systems into Ukraine in light of the concerns raised about the possible Russian use of the weapons.

In recent weeks, American officials have expressed concerns that Russia has been preparing a false-flag operation -- claiming Ukraine's use of chemical or biological weapons -- that Russia could use as a justification for its use of such weapons.

Following meetings with NATO leaders in Brussels on Thursday, President Joe Biden said the United States would respond to Russia's use of chemical and biological weapons, but did not lay out specifics for possible responses.

"We would respond if he uses it," Biden said at a news conference. "The nature of the response would depend on the nature of the use."

"We are working through contingency planning for a range of different scenarios," national security adviser Jake Sullivan told reporters traveling with the president on Friday. "In broad terms, I believe that there is convergence around the fundamental nature of how the alliance would respond to these issues."

"Any use of weapons of mass destruction, nuclear, chemical, biological, Russia would pay a severe price for the use of those weapons, as the president has previously said," Sullivan added. "We have spoken to our allies, we've done contingency planning within our own government, and we have communicated directly to the Russians."

The administration also is weighing how it would respond should Russia target the supply lines inside Poland and other NATO countries that are flowing in thousands of American-made Javelin anti-tank missiles and Stinger anti-aircraft missiles to Ukraine's military.

The administration will most likely pursue a response of "careful reciprocity" to avoid escalation according to the official. Such a response might include the proportional targeting of any Russian weapons system involved in an attack on supplies inside of Poland said the official.

Contemplating a tougher response is tempered by the reality that "everyone knows what that would lead to" said the official.