US-Israeli attacks on Iran and Tehran's retaliatory strikes have roiled markets and triggered a surge in energy prices.

EU energy commissioner Dan Jorgensen said the immediate impact on the EU's "security of supply" was contained but governments needed to prepare for a "potentially prolonged disruption of international energy trade".

"We need to act already now, and we need to act together," Jorgensen said in a statement, ahead of video talks with energy ministers from the 27-nation bloc.

To ease the impact of the war, EU countries have contributed to the release of about 400 million barrels of strategic reserves under the coordination of the International Energy Agency (IEA) -- the biggest such release ever.

But in a letter to member states seen by AFP Jorgensen urged further coordination "for an effective and efficient planning of the release of stocks".

This to optimise the demand and supply balance "for a longer period of time of, in particular, jet fuel and diesel, and the access to crude oil for refineries," he wrote.

He also called on EU governments to consider the promotion of "demand saving measures", particularly in the transport sector.

The Iran war has virtually halted activity in the strategically vital Strait of Hormuz, through which a fifth of the world's crude supplies and a substantial amount of gas normally run.

From Spain to Croatia, several member states have sought to contain energy costs with tax reductions, caps on fuel prices and other measures.