STOCKHOLM, March 9 (Reuters) - Europe became the world's biggest arms importer over the last five years as governments reacted to Russia's threat and waning confidence in U.S. security commitments, data from the Stockholm International Peace Research Institute showed on Monday.

European countries more than trebled their arms imports in 2021-25 versus 2016-2020 to supply Ukraine in its defence against Russian invasion and to rebuild their own militaries after decades of under-investment.

"The sharp increase in arms flows to European states pushed global arms transfers up almost 10 per cent," Mathew George, Director of the SIPRI Arms Transfers Programme, said.

Europe accounted for 33% of global arms imports, up from 12% in the previous five-year period, the report showed.

Despite boosting domestic production, European countries continued to increase purchases of U.S. weapons, especially combat aircraft and long-range air-defence systems.

MIDDLE EAST

Arms imports by Middle Eastern states fell 13%, though Saudi Arabia and Qatar were among the top four individual buyers.

The decline mainly reflected large Saudi orders during the previous period that still needed to be integrated, SIPRI senior researcher Pieter Wezeman said.

Even before the latest U.S. and Israeli attacks on Iran, states in the region had placed significant new orders that have yet to show up in the figures.

The current conflict is likely to lift procurement further, particularly of anti-missile and air-defence systems.

"They will first replace what they have used, but also that they are going to look at buying more equipment to protect themselves even better than they can do now," Wezeman said.

In terms of suppliers, the U.S. increased its global share of the arms export market to 42% from 36%, cementing its dominance. France was the second-largest supplier with 9.8% of global exports, while Russia's share dropped to 6.8% from 21% after its 2022 invasion of Ukraine.

Europe's combined export share was 28% - four times Russia's and five times China's.

(Reporting by Simon Johnson. Editing by Mark Potter)

((simon.c.johnson@thomsonreuters.com; +46 70 721 1045; Reuters Messaging: simon.c.johnson.reuters.com@reuters.net))