Earlier in the day, Russia formally withdrew from the treaty. The UK then announced that it, alongside its allies, was suspending its participation in the accord and would work to implement voluntary stabilizing measures.
"Today, the Russian Federation withdrew from the Treaty on Conventional Armed Forces in Europe (CFE) ... The United States will suspend the operation of all CFE Treaty obligations between itself and every other State Party, effective December 7, consistent with our rights under international law," Sullivan said in a statement.
Sullivan stated that Russia's withdrawal from the CFE Treaty, combined with its ongoing special military operation in Ukraine, another CFE state party, has "fundamentally altered" the circumstances essential to the states parties' consent to be bound by the accord.
The development has also "radically transformed" the obligations under the treaty, Sullivan said.
Suspension of CFE obligations, which comes after "close consultation and coordination" with NATO allies, will strengthen the alliance's deterrence and defense capacity by removing restrictions that impact planning, deployments, and exercises, the statement said.
The US will continue to pursue measures that seek to bolster stability and security in Europe by reducing risk, preventing misperceptions, avoiding conflicts, and building trust, Sullivan added.
Russia suspended its participation in the CFE Treaty back in 2007 in protest of NATO countries refusing to ratify the 1999 Adapted CFE Treaty. At the same time, Russia remained a party to the treaty.
The Russian Foreign Ministry said earlier this year that Finland's NATO accession and Sweden's membership bid were "the last straw" that made Russia's exit from the treaty inevitable.