Russia is scaling down its hugely successful cooperative effort with the U.S. to secure its nuclear materials, raising concerns over the safety and security of tons of dangerous nuclear materials. Security and non-proliferation experts said the move harms a global effort to secure nuclear material and could leave materials vulnerable to theft by terrorists.

Russia has decided to no longer take U.S. funding for on-site security, training and nuclear security measures at its borders under the 25-year-old Cooperative Threat Reduction program that the two countries agreed upon following the fall of the USSR in the early 1990s, according to the Boston Globe. The CTR programs were set to end in 2018, but the Russians are pulling out early amid strained relations between the two countries over the ongoing rebel crisis in Ukraine.

 “If the U.S. and Russia aren’t leading then that sets a bad example for the rest of the world. We have a special responsibility to combat nuclear terrorism,” said Andrew Bieniawski, of the Nuclear Threat Initiative in Washington, D.C. “This is an area that should not be subject to what is going on in the broader geopolitical situation.”

Over 7,500 warheads were dismantled under the CTR program since 1991, according to the U.S. Department of Defense’s Defense Threat Reduction Agency. The U.S. paid at least $2 billion since 1991 to Russia to fund security upgrades around the country over fears that terrorists could get their hands on nuclear materials through the scores of disgruntled, unpaid workers or corrupt officials in the chaos of post-Soviet Russia.

While the upgrades have vastly improved security at facilities and the border, there was more work to be done. The U.S. allocated $100 million for upgrades in 2015. But Russia's decision means joint security operations at all 18 of Russia’s civilian-run facilities holding weapons-grade materials will end and the installation of state-of-the art surveillance systems in 13 nuclear storage facilities will be canceled, along with upgrades at 7 “nuclear cities,” or the closed communities built around Russian military nuclear facilities, according to RT.

Many doubt Russia will continue to fund these projects to the extent needed to maintain security. In July, the U.S. Department of Energy warned that “securing these stockpiles will not [be done] to the standards necessary unless the United States continues to invest."

The CTR programs were never popular with hawkish politicians in either country. In Russia, taking on the projects independently was a matter of pride and practicality. It allowed Russia to move past the embarrassing 1990s and would keep U.S. eyes out of sensitive military and nuclear facilities, said Nikolai Sokov, a senior fellow at the Vienna Center for Diarmament and Non-Proliferation.

“Now that they won’t allow access, it begs the question, how do you gain confidence that all these upgrades are being sustained and put in use?” Bieniawski said. 

The Russian government is tight-lipped about their stores of nuclear material, but as of 2012 there were around 4,000 warheads were retired and awaiting dismantlement, according to CNN. As far as active and stockpiled operational warheads, Russia has around 8,000, or just under half of the global total. The U.S. has much of the other half: around 7,300.

Russia also has around 695 metric tons of weapons grade highly enriched uranium and 128 metric tons of military use plutonium, according to the Nuclear Threat Initiative. About 25 kilograms of highly enriched uranium is needed to create a traditional nuclear weapon.

There is at least 300,000 cubic meters of low and medium-grade nuclear materials waiting to be placed in repositories in Russia, which likely can’t be used to build a traditional nuclear weapon, but could be used to build a “dirty bomb,” or a conventional bomb laced with radioactive material. The Islamic State militant group claimed to have made a dirty bomb late last year with as little as 40 kilograms of uranium, although those claims have not been confirmed. 

For comparison, all nuclear facilities worldwide produce around 200,000 cubic meters of low and intermediate-level waste every year.

Russia’s national waste management agency said in October its main problems moving forward include problems managing the local authorities where waste will be located and a lack of funding for the communities surrounding the proposed sites, according to World Nuclear News.

Even with the upgrades, smugglers are still trying to their hands on materials. Hundreds of plots to steal or buy nuclear materials in Russia were reported in the 2000s and were foiled with the help of the American entities.

More recently, in 2010, Armenian officials arrested a man trying to sell highly enriched uranium for the second time, which he said he got from a supplier who himself got the material from “contact” in the Russian Urals region and Siberia. He was caught the first time at the Armenian-Georgian border when his smuggled stock set of radiation detectors, but he was able to bribe himself out of detention, possibly even keeping some of his materials, according to the Guardian

The risk of a successful smuggling operation is increased now that the U.S. will not help oversee the implementation of security measures, experts said. Shota Utiashvili, head of analysis for Georgia’s interior ministry, said after the 2010 arrest that “the level of corruption in Russia and the increasing immunity of senior officers means that they may well try to sell this stuff again.”

Nuclear cooperation has long been a landmark of the sometimes contentious Russo-American relationship, because it always continued despite any political tensions between the nations. Along with the Strategic Arms Reduction Treaty and the Treaty on the Non-Proliferation of Nuclear Weapons, the CTR program ensured that the U.S. and Russia would put their differences aside to ensure nuclear security.

“As the two largest possessors of fissile material on the planet, the United States and Russia have a responsibility to continue to ensure the highest standards of security for these materials,” said Kingston Reif, director for disarmament and threat reduction policy at the Arms Control Association in Washington, D.C.