All nuclear-armed countries continue to either develop new weapons or upgrade existing stockpiles, despite an international trend toward disarmament, according to a new report by the Stockholm International Peace Research Institute (SIPRI). The report, published Monday, assesses the current state of nuclear armament as the number of peace operations increases around the world.

At the beginning of 2015, nine nuclear-armed states, including the United States, Russia, the United Kingdom, France, China, India, Pakistan, Israel and North Korea, possessed nearly 15,850 nuclear weapons, of which 4,300 were deployed with operational forces and 1,800 were kept in a state of high operational alert, the SIPRI report said. While the number of nuclear warheads has fallen in recent years -- with the U.S. and Russia representing the bulk of the reduction -- the modernization and development of nuclear weapons are still underway in all these countries, according to the report.

“Despite renewed international interest in prioritizing nuclear disarmament, the modernization programs under way in the nuclear weapon-possessing states suggests that none of them will give up their nuclear arsenals in the foreseeable future,” Shannon Kile, a senior researcher at SIPRI, said, in a statement.

Although the U.S. and Russia continue to reduce their nuclear arsenals, both countries are also working on “extensive and expensive long-term modernization programs,” according to the report. At the same time, other nuclear-armed nations are either developing or deploying new nuclear weapons, or have announced their intention to do so.

“In the case of China, this may involve a modest increase in the size of its nuclear arsenal,” the report said. “India and Pakistan are both expanding their nuclear weapon production capabilities and developing new missile delivery systems.”

Meanwhile, North Korea is believed to be developing its nuclear arsenal of six to eight warheads, but SIPRI said the country’s “technical progress” was difficult to assess.

nuclearweaponslist-SIPRI World nuclear forces, 2015. Photo: Stockholm International Peace Research Institute

The SIPRI report comes after the National Council of Resistance of Iran (NCRI), a Paris-based Iranian dissident group, claimed last month that North Korea and Iran were secretly building ties to equip themselves with ballistic missiles and nuclear warheads. According to NCRI, a delegation of nuclear arms experts from North Korea visited a military site near Tehran in April while Iran was in talks with world powers over its nuclear program.

Iran and six world powers are expected to reach a final comprehensive settlement over a proposed nuclear deal by the end of June. The move is aimed at persuading the Islamic nation not to develop nuclear weapons in exchange for the lifting of international sanctions.