Updated

Iran has increased its stockpile of uranium enriched to higher levels, the country's nuclear chief said Saturday, in defiance of U.N. demands to halt the program.

Vice President Ali Akbar Salehi also said Iran has built a plant to make nuclear fuel plates and rods in Isfahan. That would allow Iran to produce its own reactor fuel and give it more leverage against the West. But Western experts have disputed whether Iran has the technological capability to produce plates and rods when Tehran made similar claims in the past.

Iran's refusal to stop enrichment lies at the heart of its dispute with the West over the country's nuclear program.

Salehi, who is also Iran's acting foreign minister, said Tehran now has 40 kilograms of uranium enriched to 20 percent, up from 30 kilograms reported in October.

Uranium enriched to 20 percent is enough to produce fuel for a medical research reactor but far below the more than 90 percent required to build fissile material for nuclear warheads.

A deal for the West to provide fuel for the reactor has fallen apart in the deadlock over Iran's broader nuclear program, which the West suspects is designed to develop atomic bombs. Iran denies the allegations, and says the program is peaceful.

Iran says fuel for the Tehran research reactor that produces the medical radioisotopes will run out in September, leaving it without the materials needed to diagnose and treat 850,000 cancer patients across the country.

"We've produced nearly 40 kilograms of 20 percent enriched uranium. We hope to inject the first Iranian-made fuel assembly into the Tehran reactor by September," the semiofficial Fars news agency quoted him as saying.

Salehi said Iran initially had no intention to enrich uranium to 20 percent but was forced to do so after world powers refused to provide it nuclear fuel.

The U.N. Security Council imposed a fourth round of sanctions this summer against Iran over its refusal to halt uranium enrichment, which can be used to produce nuclear fuel or materials for bombs.

Iran started producing the 20 percent-enriched material in February 2010, saying the production rate was about three kilograms (6.6 pounds) each month.

Iran is producing the 20 percent level from its own stocks of low-enriched uranium, which has a 3.5 percent purity and is needed to fuel an electricity-generating reactor.

Salehi insisted Saturday — something Iran has been claiming for months — that it has the rare technology needed to produce the fuel rods.

"We've set up an advanced plant to produce fuel plates in Isfahan," he said. "With the completion of this plant in Isfahan, we are among few countries that can produce both fuel rods and fuel plates," Fars quoted him as saying.

Production of fuel rods by Iran would give it an independent source of fuel for the Tehran research reactor and future nuclear power plants — and another bargaining chip in negotiations with the West.

"The more they delay the talks, we will move forward. After some time, the issue of fuel swap will be meaningless," Salehi was quoted as saying.