BRUSSELS - Europe must race to replace sanctioned and curtailed Russian energy supply and should double down on efficiency and renewables, including nuclear power, the International Energy Agency (IEA) said on Wednesday.

Gas prices have hit record levels as a slowdown in flows from Russia in recent days has deepened worries over supply in higher-demand winter months.

"In the near term, the scramble for alternative sources of fossil fuels creates clear openings for non-Russian suppliers," the Paris-based watchdog said in its annual report on investment.

Europe must react to the crisis "with a determined acceleration of investment in efficiency, renewables and other clean technologies," it added.

The EU and other developed economies have sanctioned Russian oil and coal but have held off on banning gas imports.

Shoring up ageing nuclear infrastructure might provide a respite to soaring power prices and tight supply, the IEA said.

"In light of renewed interest in nuclear power's role in clean energy transitions, the war has underscored the need to explore options for ... investment in new facilities as well as the reopening of existing (uranium) conversion plants."

More broadly, $2.4 trillion set to be invested in energy this year included record spending on renewables but fell short of plugging a supply gap and tackling climate change, the agency said.

Rising 8% from the previous year, when the pandemic was more severe, the investment included big increases in the electricity sector and efforts to bolster energy efficiency, it said.

"This kind of investment is rising, but we need a much faster increase to ease the pressure on consumers from high fossil fuel prices, make our energy systems more secure, and get the world on track to reach our climate goals," said IEA Executive Director Fatih Birol.

Investment in oil and gas, on top of setting back efforts to reach climate goals, could not meet rising demand if energy systems were not retooled towards cleaner technology

"Today's oil and gas spending is caught between two visions of the future: it is too high for a pathway aligned with limiting global warming to 1.5 degrees C but not enough to satisfy rising demand in a scenario where governments stick with today's policy settings and fail to deliver on their climate pledges," the agency said.

(Reporting by Noah Browning Editing by Mark Potter and Bradley Perrett)