Israel will not press Washington to tighten sanctions on Iran while nuclear negotiations continue for the next six months, but will push for tough action if the talks' June deadline is not met, a senior Israeli official said on Thursday.

Intelligence Ministry Director-General Yuval Wollman's remarks suggested cautious confidence Washington will stick to demands that Iran curb its atomic work, although any deal is unlikely to meet Israel's original call that Tehran's nuclear program be dismantled.

Iran denies Western accusations it is seeking nuclear weapons and says it has a sovereign right to a civilian program. Talks between Iran and six world powers, including the United States, have been extended beyond two previous deadlines since February.

"Within the framework of the extended talks, we think what is right is a steady and strong sanctions regime," Wollman told Reuters in an interview. "We are not dealing with additional sanctions now. I know of no [Israeli] position calling for that, officially or unofficially."

Israel, believed to have the region's only atomic arsenal, is not a party to the negotiations but wields influence due to its close relations with Washington and its threats to launch preemptive strikes on Iran to stop it getting nuclear weapons, if diplomacy fails.

If a deal is not struck by June 30, the latest deadline, Israel wants world powers to cancel limited sanctions relief granted Iran under a 2013 interim deal, Wollman said.

A more right-leaning Congress that will be inaugurated in Washington next month is likely to back tougher measures, he said, including "third party" sanctions under which Washington would penalize foreigners doing business with Iran.

"When a country asks itself, 'Do I want to develop economic ties with Iran, at the cost of economic ties with the United States?' That's not such a difficult question," Wollman said.

"The United States has yet to exhaust its ability to toughen matters for Iran."

He played down any possibility President Barack Obama, now in his second term, might veto anti-Iran legislation in order to secure a nuclear deal considered insufficient by Israel.

"We believe and we see that the American administration is listening to us, is open with us and is conducting a very positive dialogue with us. So we hope that, if a deal is signed, it will be a good deal," he said.