Israeli Prime Minister Benjamin Netanyahu said on Wednesday that Iran had expanded its sensitive enrichment of uranium despite the election as president of moderate cleric Hassan Rowhani.

"Iran has not stopped its nuclear programme, even after its presidential election" on June 14, Netanyahu said in comments broadcast by public radio.

"At the moment, they are using 7,000 new centrifuges, including 1,000 which are of a newer type," he said on a visit to southern Israel.

"The Iranian president is trying to present a new image... but the nuclear programme's progress continues."

On Tuesday, Rowhani said Iran was ready to hold "serious" talks with the major powers without delay to allay Western concerns about its nuclear programme.

But he underlined that Iran would not abandon uranium enrichment, the sensitive activity at the heart of Western concerns which it suspended when Rowhani was chief nuclear negotiator a decade ago.

Iran said in March that it intends to install around 3,000 new-model centrifuges at a nuclear plant near the central town of Natanz enabling it to speed up the enrichment of uranium.

Around 13,500 older-model centrifuges are already in place at the plant.

The UN Security Council has passed repeated resolutions calling on Iran to suspend all enrichment and has imposed four rounds of sanctions.

The Iranian president warned on Tuesday that negotiations would not work under pressure but the Israeli premier took issue with that position.

Rowhani "tells us that no threat will deter him. This is false," Netanyahu said.

"The only thing in the past 20 years that has forced the Iranians to stop their nuclear programme is pressure and explicit threats of military operations," he said.

Netanyahu said on July 14 that Israel may be forced to act before the United States does over what it fears is a covert drive by Iran for a nuclear weapons capability.

Israel, which has the region's sole if undeclared nuclear arsenal, regards a nuclear-armed Iran as a threat to its very existence.

Even before Rowhani took office on Saturday, Netanyahu kept up Israel's tough rhetoric. He has called Rowhani a "wolf in sheep's clothing" who would "smile and build a bomb."