"The right path is the one marked by the New Start Treaty," Mogherini stated at the Carnegie Endowment for International Peace 2017 Nuclear Policy Conference.
Mogherini added that Europe and Russia have also cooperated successfully on nuclear issues, including the 2015 Iran nuclear deal.
However, she claimed, a new arms race between the United States and Russia would destabilize entire regions and threaten security.
In January, US Secretary of State Rex Tillerson said during his confirmation hearing that the United States must stay engaged with Russia on the New START treaty and ensure both sides meet their respective obligations.
New START was signed by the United States and Russia in 2010 with the goal of cutting the number of deployed nuclear warheads to 1,550 by 2018.