Iran's national electricity company Tavanir said power cuts affecting parts of central Tehran on March 23 were caused by a routine grid fault and were not the result of a military strike, Mehr reported.

The statement came after residents reported outages in several central districts, prompting concern that the blackouts could be linked to the US-Israeli military campaign.

"There has been no attack or incident on the power grid across the capital. The disruption was caused by normal network errors," Tavanir said, adding that the problem had been largely resolved and the grid was returning to stable conditions.

The reassurance carries heightened significance as Trump's 48-hour ultimatum threatening to strike Iranian power plants "starting with the biggest one first" was due to expire on March 24. Iran's parliament speaker Ghalibaf warned that any attack on energy infrastructure would trigger "irreversible" destruction of Gulf oil and gas facilities.

Israeli strikes have already knocked out up to half of Iran's South Pars gas processing capacity, and a missile landed 200 metres from the Bushehr nuclear reactor on March 18.

Tehran's governor urged residents last week to conserve petrol and reduce unnecessary travel.

Iran's power grid has been under strain for years due to ageing infrastructure, rising demand and reduced gas supplies.

The war has added further pressure, with the South Pars damage threatening the gas supply that fuels a significant share of the country's electricity generation.