A top Iranian official says a nuclear fuel swap with the West proposed under a U.N.-drafted plan remains an option.

The late Tuesday comment by Ali Akbar Salehi, Iran's nuclear chief and a vice president, came hours after Iran began enriching uranium to about 20 percent over objections from the U.S. and its allies who fear the process could be used to make nuclear weapons.

On Wednesday, Salehi was quoted by state TV as saying the enriching process was "moving forward smoothly."

Under the U.N. plan, Iran would send its stockpiled, low-enriched uranium abroad for processing into fuel rods to power a research reactor thus denying Iran the ability to enrich those stocks to higher levels needed for making warheads.