Iran’s chief negotiator in nuclear talk has warned that Tehran is ready to walk away if “excessive” Western demands cause a failure, eight days before a deadline for a deal.

Abbas Araqchi said however that he hoped that the attendance from Sunday of foreign ministers in Vienna including US Secretary of State John Kerry would help overcome “deep differences” that remain.

“If we see that the excessive demands (of Western powers) persisting and that a deal is impossible, this is not a drama, we will continue with our nuclear program,” Araqchi said.

“The presence of ministers will have a positive influence,” he told Iran state television from the Austrian capital.

“There are questions that ministers need to take decisions on.”

Iran’s talks with the five permanent members of the UN Security Council plus Germany are aimed at a grand bargain reducing in scope Iran’s nuclear activities in return for sanctions relief.

Such a deal is meant to quash for good concerns about the Islamic republic getting the bomb after more than a decade of failed diplomacy, threats of war and atomic expansion by Iran, although Iran denies wanting nuclear weapons.

The deadline for an accord is July 20, when an interim accord struck by foreign ministers expires, although this can be put back if both sides agree.

On Friday, William Burns, Washington’s pointman in secret 2013 talks with Iran that helped produce the November deal, said that the differences between the two sides remain “quite significant”.

“I would say that there is a lot of ground that has to be covered if we’re going to get to a comprehensive agreement,” Burns told Indian channel NDTV according to a State Department transcript.

“We need to continue to work at it and we’re determined to do that,” he said.

Kerry was expected late on Saturday or early on Sunday in Vienna where he will be joined by his British, French and German counterparts William Hague, Laurent Fabius and Frank-Walter Steinmeier.