STOCKHOLM (Reuters) - The world's 100 biggest defence equipment makers increased their arms sales by 4.2% in 2023 to $632 billion, fuelled by wars and regional tensions, a leading think-tank said on Monday.

The Stockholm International Peace Research Institute (SIPRI) said in a report U.S. groups on the list grew sales by 2.5% in total compared to the year before to $317 billion. Market leaders Lockheed Martin ( LMT ) and RTX however saw slightly lower arms sales.

The rise followed a 3.5% dip in arms sales in 2022, which SIPRI has blamed on labour shortages, supply-chain disruptions and rising costs, which made it hard for many companies to meet increased demand driven by Russia's invasion of Ukraine.

European companies on the list - excluding Russian - had roughly unchanged combined sales in 2023 at $133 billion, but order intake surged, and some groups saw a surge in demand linked to the war in Ukraine.

Earlier this year, SIPRI reported a 7% increase in global military spending in 2023, the steepest annual increase since 2009.

"Overall, smaller producers were more efficient at responding to new demand linked to the wars in Gaza and Ukraine, growing tensions in East Asia and rearmament programmes elsewhere," SIPRI said.

The Russian groups on the list, including state-owned Rostec, accounted for the biggest combined rise - 40% to $26 billion.

"The arms revenues of the Top 100 arms producers still did not fully reflect the scale of demand, and many companies have launched recruitment drives, suggesting they are optimistic about future sales," SIPRI researcher Lorenzo Scarazzato said.