Lead US Iran negotiator, Under Secretary of State Wendy Sherman, is expected to brief Congressional leaders and relevant committee chiefs in classified session this week on the talks between six world powers and Iran held in Geneva last week.

In a brief conversation last week that did not delve into the details of the Iranian proposal, Sherman told House Foreign Affairs Committee ranking Democrat Eliot Engel “that the Iranians appeared serious,” but cautioned that the “devil’s in the details and made clear that the US negotiators will remain clear eyed as they seek to negotiate a deal to end Iran’s nuclear weapons program,” Engel said in a statement.

“Ranking Member Engel was pleased that the P5+1 reportedly had a productive first round of negotiations with the Iranians in Geneva,” spokesman Daniel Harsha told Al-Monitor Monday. “But a change in tone is hardly sufficient. He believes pressure brought Iran to the table, and that pressure must be maintained until Iran has verifiably dismantled its nuclear weapons program.“

“The Iranians are masters at negotiation for the sake of buying time," Harsha said. "Given that, Ranking Member Engel would only be open to freezing further legislative action on the new sanctions bill if Iran quickly takes a number of concrete and fully verifiable steps to freeze enrichment and other elements of its nuclear weapons program. And he won’t even consider easing sanctions already on the books until Iran verifiably dismantles their program, leaving absolutely no possibility of a rapid ‘breakout.’”