STOCKHOLM The number of operational nuclear weapons rose slightly in 2022 as countries implemented long-term force modernisation and expansion plans, a leading conflict think-tank said on Monday, warning that the world was entering a dangerous phase.

The estimated number of warheads in military stockpiles for potential use rose by 86 to 9,576, the Stockholm International Peace Research Institute (SIPRI) said in a statement, continuing a trend seen in the last couple of years.

"We are drifting into one of the most dangerous periods in human history," SIPRO Directo Dan Smith, SIPRI Director.

"It is imperative that the world's governments find ways to cooperate in order to calm geopolitical tensions, slow arms races and deal with the worsening consequences of environmental breakdown and rising world hunger."

The nine nuclear-armed states continued to modernize their nuclear arsenals and several deployed new nuclear-armed or nuclear-capable weapon systems in 2022, SIPRI said.

Russia and the United States together possess almost 90% of all nuclear weapons but the think tank said the sizes of their respective arsenals appeared to have remained relatively stable in 2022.

Overall, the number of nuclear warheads in the world continued to decline, primarily due to the USA and Russia dismantling retired warheads.

(Reporting by Johan Ahlander; editing by Philippa Fletcher)