The U.S. announced Friday it will suspend its participation in a Cold War-era ballistic missile treaty Feb. 2 over alleged Russian violations of the pact. 

In announcing the departure, Secretary of State Mike Pompeo accused Russia of consistently violating the terms of the landmark 1987 Intermediate-Range Nuclear Forces (INF) Treaty "without remorse," and said Moscow remains in "material breach" of its obligations. 

The formal exit has been expected for nearly four months. 

President Donald Trump announced in October that Washington would be exiting the INF Treaty which eliminated all U.S. and Russian ground-launched cruise missiles with ranges of 310-3,420 miles (500-5,500 kilometers) and their launchers, citing alleged Russian violations of the pact.

Pompeo in December gave Russia two months to return to full compliance with the agreement, but said Friday it had not done so. 

"Russia has refused to take any steps to return real and verifiable compliance over these 60 days," he said. 

Russia has denied being in non-compliance with the INF's terms. But Washington and its NATO allies point to its development of the Novator 9M729 missile, also known by its NATO designation SSC-8, as violating the INF's terms.

The Trump administration's announcement starts a six-month process for withdrawal under the INF's terms.

Shortly after his top diplomat addressed reporters, Trump said if Russia returns to compliance "by destroying all of its violating missiles, launchers, and associated equipment," the U.S. will not leave the agreement, but said Moscow has been "covertly developing and fielding a prohibited missile system that poses a direct threat to our allies and troops abroad."

"We cannot be the only country in the world unilaterally bound by this treaty," he said in a statement. "We will move forward with developing our own military response options and will work with NATO and our other allies and partners to deny Russia any military advantage from its unlawful conduct."

The Transatlantic Alliance said in a statement that the 9M729 "poses significant risks to Euro-Atlantic security," urging Russia to return to compliance with the INF. 

"Unless Russia honours its INF Treaty obligations through the verifiable destruction of all of its 9M729 systems, thereby returning to full and verifiable compliance before the U.S. withdrawal takes effect in six months, Russia will bear sole responsibility for the end of the Treaty," NATO said.