Researchers said that the decline in the number of nuclear weapons seen since the early 1990s has slowed, with some indications of an increase.

"It seems that the reduction in nuclear arsenals to which we have become accustomed since the end of the Cold War seems to be waning," said Hans Christensen from the Stockholm International Peace Research Institute (SIPRI).

The total number of nuclear weapons among the nine nuclear-armed countries, the United States, Russia, Britain, France, China, India, Pakistan, Israel, and North Korea, was 13,080 in early 2021, a slight decrease from 13,400 in the previous year, according to a SIPRI report.

"We see very important nuclear modernization programs all over the world and in all the nuclear states," Christensen added. He also said that nuclear states appear to be raising the "importance they attach to nuclear weapons in their military strategies."