"At the moment technically they are in compliance" with they Joint Comprehensive Plan of Action (JCPOA), Haspel told the Senate Intelligence Committee.

"I think the most recent information is the Iranians are considering taking steps that would lessen their adherence to JCPOA as they seek to pressure the European to come through with the investment and trade benefits that Iran hoped to gain from the deal," she said.

"They are making some preparations that would increase their ability to take a step back if they make that decision," she noted.

"But we do see them debating amongst themselves as they failed to realize the economic benefits that they hoped for from the deal."

The United States withdrew from the JCPOA on May 8, 2018, after President Donald Trump concluded it was not in US interests. The administration argued that the windfall from trade would go to finance Iran's regional military activities, and there was no guarantee it would not resume nuclear weapons development after the deal expired.

Washington has since restored tough sanctions that were in place before the deal was reached.

The remaining five signatories to the JCPOA -- Britain, China, France, Germany and Russia -- have distanced themselves from Trump's move and have supported continued commercial engagement with Tehran.

But, as a number of European companies have pulled out under pressure from US sanctions, those countries have backed an EU effort to set up a special payment system in an attempt to continue trade and business ties with Iran.