Landmark Cold War-era arms-control pact officially dead, fueling fears of new nuclear arms race The U.S. withdrew after repeatedly calling Russia in violation.

The United States will withdraw from a landmark Cold War arms-control pact on Friday, six months after the Trump administration declared Russia in material breach of the treaty and said Moscow hadn't made an effort to return to compliance.

The death of the Intermediate-Range Nuclear Forces Treaty marks a dangerous new era of nuclear threats, analysts and former officials said. But senior administration officials argue the U.S. had no choice but to terminate a deal that only one side was abiding by.

"Russia is solely responsible for the treaty’s demise," Secretary of State Mike Pompeo said in a statement Friday. "The United States will not remain party to a treaty that is deliberately violated by Russia."

The secretary of state, currently in Bangkok for a summit between Asian countries, tweeted out comment on the end of the treaty immediately after it ended.

Pompeo first put Moscow on notice in December after NATO's foreign ministers issued a joint declaration that a new Russian missile system had violated the pact signed by President Ronald Reagan and Soviet leader Mikhail Gorbachev. Shortly after the declaration, Pompeo gave Russia a 60-day deadline to return to compliance.

In February, the Trump administration officially began the six-month withdrawal process, notifying Moscow of its intent to leave the treaty, but leaving the door open to staying if Russia agreed to comply.

Russian President Vladimir Putin and his government have long denied violating the pact, which banned ground-launched cruise missiles with a range between 310 and 3,100 miles -- whether nuclear-armed or conventional.

The Obama administration first accused Russia of violating the INF Treaty in 2013, specifically pointing to the development and deployment of the 9M729 missile system. Despite top-level appeals from the U.S. on multiple occasions, Russia denied the system existed, before later saying it didn't violate the treaty's terms.

"To date, Russia has produced and fielded multiple battalions of the 9M729 ground-launched cruise missile, throughout Russia, in violation of the INF Treaty, including missiles fielded in western Russia with the ability to strike critical European targets," a senior administration official said Thursday.

Despite Pompeo's 60-day ultimatum and the six-month wind-down period, "Russia has made no effort" to come into compliance.

Senior administration officials said they did not know if there was a specific time the treaty would expire, but that the U.S. would consider the treaty to have ended on Friday.

There were no plans to communicate directly with Russia about the termination after the U.S. sent a diplomatic note to the Russians in February. President Donald Trump and Putin spoke by phone on Wednesday, but Trump told reporters that the two didn't discuss the INF Treaty.

"Russia would like to do something on a nuclear treaty, and that's OK with me," the president added on the White House South Lawn Thursday, sounding optimistic about future talks.

In particular, U.S. officials seemed to hope Russia will help the U.S. pressure China, itself with a growing arsenal, to join arms-control pacts that the two Cold War-era enemies were party to. The senior official said there have been "regular conversations" with Russia and China regarding trilateral arms control.

There are few public signs such negotiations are advancing. An American delegation, led by Deputy Secretary of State John Sullivan and Andrea Thompson, undersecretary for Arms Control and International Security, met their Russian counterparts in Geneva on July 17 and "made clear that a commitment to full and verifiable treaty compliance is necessary for effective arms control. The U.S. delegation also underscored concerns about Russia's development and deployment of non-strategic nuclear weapons and lack of transparency with regard to existing obligations," the State Department said.

Critics also have said the Trump administration, which has struggled to negotiate with North Korea and has been ignored by Iran, hasn't shown a capacity for arms-control negotiation.

"This administration simply does not have the personnel or the capability or the process in place to achieve any of that," said Jon Wolfsthal, who served as President Barack Obama's senior director for arms control and nonproliferation at the National Security Council.

Until then, arms-control experts warn, the world now faces a dangerously heightened risk from nuclear weapons and a possible new arms race.

"Nuclear issues are so consequential that we simply cannot abandon a serious arms control effort," said Laura Kennedy, former U.S. envoy to the Conference on Disarmament in Geneva. "Engagement alone won't solve these serious issues but without such diplomacy, no sound solution is possible."

"Not since the 1962 Cuban missile crisis has the risk of a U.S.-Russian confrontation involving the use of nuclear weapons been as high as it is today," former Energy Secretary Ernest Moniz and former Sen. Sam Nunn, co-chairs of the nonprofit Nuclear Threat Initiative, wrote in a forthcoming Foreign Affairs article.

"Unlike during the Cold War," they added, "both sides seem willfully blind to the peril."