President Joe Biden signaled a tougher U.S. stance on Russia on Tuesday in his first phone call with President Vladimir Putin, raising concerns over human rights and “aggression” against Ukraine, but welcoming cooperation on a new nuclear weapons accord.

The call was initiated by the White House to discuss progress on extending the New START deal, which limits the two powers to a maximum of 1,550 deployed nuclear warheads each and expires February 5.

In Washington, a State Department official who asked not to be identified said the two sides had “reached agreement… to proceed quickly to conclude such an agreement by February 5.”

The moves raised hopes for more stability between the world’s two most heavily armed nations, drawing a line under the uncertainty that entered under Donald Trump, whom Biden replaced just last week. The moves raised hopes for more stability between the world’s two most heavily armed nations, drawing a line under the uncertainty that entered under Donald Trump, whom Biden replaced just last week.