"The cascade of decisions by EU companies to end their activities in Iran makes things much more complicated," Zarif told reporters.

He spoke after meeting with EU energy commissioner Miguel Arias Canete, who has been on a two-day visit to Tehran -- the first by a Western official since Washington announced its withdrawal from the 2015 nuclear deal earlier this month.

"With the exit of the United States from the nuclear deal, the expectations of the Iranian public towards the European Union have increased... and the EU's political support for the nuclear agreement is not sufficient," Zarif added in comments carried by state broadcaster IRIB.

Several foreign firms have already halted their Iranian operations while they wait to see how talks within the EU will play out.

French oil major Total said last week it would abandon its $4.8-billion investment project in Iran unless it was granted a waiver from Washington.

Another French energy giant, Engie, said Saturday it would cease engineering work in Iran before November, when US sanctions are due to be reimposed.

"The European Union must take concrete supplementary steps to increase its investments in Iran. The commitments of the EU to apply the nuclear deal are not compatible with the announcement of probable withdrawal by major European companies," Zarif said.

Canete said he recognised that time was short and that clear measures were needed from Europe to protect investments and oil purchases.

Iran has threatened to resume industrial uranium enrichment "without limit" if its interests are not protected.

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TOTAL

Engie