Pope Leo XIV warned on Wednesday of the risk of “a new arms race” as the last remaining U.S.-Russia nuclear treaty is set to expire.

New START, the final nuclear arms control agreement between Washington and Moscow after decades of Cold War-era accords, is due to lapse on Thursday, along with restrictions on the world’s two leading nuclear powers.

“I urge you not to abandon this instrument without seeking to ensure that it is followed up in a concrete and effective manner,” the American pope said during his weekly general audience.

“The current situation requires us to do everything possible to avert a new arms race, which further threatens peace between nations,” he added.

Leo, the Catholic Church’s first American pontiff, said it was “more urgent than ever to replace the logic of fear and mistrust with a shared ethic capable of guiding choices toward the common good.”

The Kremlin has offered a one-year extension of the treaty, but while U.S. President Donald Trump said in September that extending New START “sounds like a good idea,” little has changed since then.

The treaty, which included a monitoring mechanism, was signed in 2010 by then-Russian President Dmitry Medvedev and his U.S. counterpart Barack Obama.

Russia suspended monitoring inspections during the COVID-19 pandemic, and talks on extending the agreement have since broken down amid tensions over the Ukraine war. Moscow has also accused Washington of impeding monitoring missions on U.S. soil.

In 2023, Russia froze its participation in New START but has continued to voluntarily adhere to the treaty’s limits. Last year, Moscow tested its latest nuclear weapon carriers without atomic warheads, while Trump said he had moved two nuclear submarines closer to Russia.