Tehran, Iran: There are some in Tehran convinced a final nuclear deal between Iran and world powers has already been sealed. Others are adamant there will never be a pact.

But as uncertainty persists over talks aimed at ending the 12-year standoff on Iran's disputed atomic programme, hurdles to an agreement are stacking up.

In Washington, lawmakers are considering imposing new sanctions on Tehran despite calls from the White House to give the negotiations more time.

Although the June 30 deadline for a final agreement between Iran and the P5+1 powers -- Britain, China, France, Russia and the United States plus Germany -- is some way off, two earlier deadlines were missed.

In the Iranian capital, officials say the United States and other world powers need to show more flexibility in nailing down the hard details of a deal.

Iran's negotiators have given no indication a compromise is in the offing and supreme leader Ayatollah Ali Khamenei, who has the final word, last month voiced doubt that the US could be trusted.

Time for a 'positive signal'

Evidence of the souring atmosphere was clear when 21 hardline lawmakers recently condemned Zarif for taking a 15-minute stroll with US Secretary of State John Kerry during a break at negotiations in Geneva.

Kerry and Zarif may meet again this week in Munich and the two "need to thrash this out directly, hopefully through less controversial walks," Randjbar-Daemi said.

Amir Mohebbian, a Tehran-based analyst close to hardliners and several top figures, said the growing pressure could actually push the discussions forward.

Iranians will now be looking for signs of more concrete progress, Mohebbian said.