A sanctions relief package offered to Iran as part of nuclear negotiations could be worth up to $40 billion to Tehran, or 40 percent of the impact of the sanctions, an Israeli cabinet minister said on Wednesday.

Israel is strongly opposed to a package of sanctions relief, which the United States says will be limited and reversible, offered to Iran by global powers at talks in return for constraints on Tehran's nuclear programme.

Israeli Strategic Affairs Minister Yuval Steinitz said Israel believed the sanctions put in place by the US and European Union last year cost Iran's economy around $100 billion per year, or nearly a quarter of its output.

"The sanctions relief directly will reduce between 15 to 20 billion dollars out of this amount," Steinitz said on Wednesday at an English-language event hosted by the Jerusalem Press Club.

He said that the proposed changes would also make it more difficult to enforce other sanctions, providing a total benefit to Tehran of up to $40 billion.

"The damage to the overall sanctions, we believe, will be something between $20 billion and maybe up to $40 billion," he said.

"This is very significant. It's not all the sanctions. It's not the core sanctions about oil exports and the banking system, but it's very significant relief for the Iranians."

The United States, Britain, France, Germany, Russia and China have offered at talks to reduce sanctions in return for curbs to Iran's nuclear programme, which Western countries suspect is part of an effort to develop a nuclear bomb but Tehran says is peaceful.

The talks broke up without a deal on Saturday, but are scheduled to resume on November 20 and the sides say they are optimistic that progress can be made.

Several Western officials contacted by Reuters declined to confirm or deny specific figures for the value of the sanctions relief on offer and cautioned against revealing the terms of a hypothetical deal at such an early stage.

"There is an offer on the table, and it seems to me that is considerable progress. We can't give any technical details and the day anything leaks out is the day someone wants the negotiations to fail," said a Western diplomat.

Meanwhile,  the head of the UN nuclear agency said he saw no "radical" change in Iran's nuclear programme in the past three months, broadly covering the period since relative moderate Hassan Rouhani became president.

Yukiya Amano, director general of the International Atomic Energy Agency, told Reuters in an interview that the Islamic state was continuing its most sensitive nuclear activity, enrichment of uranium to a fissile concentration of 20 percent.

Amano also said Iran still has "quite a lot to do" in order to complete the Arak research reactor, a plant which is of deep concern to the West as it can produce potential bomb material once it is operating. Iran says its nuclear programme is entirely peaceful. - Reuters