Iran will increase its level of uranium enrichment if world powers continue to place pressure on the country over its nuclear program, a senior cleric warned Saturday.

"Iran is now capable of enriching uranium at a 20-percent level, but if they (world powers) continue their pressure, we will increase enrichment levels to 56 percent," said Reza Taqavi, a close aide to Supreme Leader Ayatollah Ali Khamenei.

The remarks, carried by ISNA news agency, followed media reports that parliament was preparing a bill urging the defense ministry to design nuclear-powered ships, whose fuel would require enriching uranium to over 50 per cent.

World powers are demanding that Iran immediately halt the 20-per-cent enrichment of uranium, which Tehran insists is for civilian purposes only.

Iranian officials maintain that the country would make some concessions if its right to pursue civilian nuclear projects was acknowledged and Western sanctions were lifted.

The next round of nuclear negotiations between Iran and the world powers will be held on Tuesday (July 24) in Istanbul, at the deputy negotiator level.

Iran will be represented by Ali Baqeri and its world negotiating partners by Helga Schmid, deputy to EU Foreign Policy Chief Catherine Ashton. Their aim is to establish whether nuclear talks could resume at the top level.