Vienna: Laborious talks towards a deal ending a 13-year standoff over Iran`s nuclear programme looked set Friday to slip into a third successive weekend with both Tehran and Washington upping the ante.
In the latest in a string of extensions, the European Union and the United States prolonged the terms of a 2013 interim deal to Monday, effectively making that the tentative new target date.
On Friday morning a deadline to present the deal to the US Congress was missed, doubling the time for American lawmakers to review the accord -- if it can be reached -- to 60 days and risking delaying key measures such as the lifting of sanctions.
"We`re making progress, it`s painfully slow... there are still some issues that have to be resolved," said British Foreign Secretary Philip Hammond, after meeting with other ministers in Vienna on Friday on a 14th day of talks.
But he voiced hope that over the next 12 hours experts working behind the scenes "will clear some more of the text and then we can re-group tomorrow (Saturday) to see if we can get over the last hurdles."
The grand bargain being sought by Iran the P5+1 --Britain, China, France, Germany, Russia and the United States -- would curb Iran`s nuclear programme in exchange for relief from painful sanctions.
Almost two years after Hassan Rouhani`s election as Iranian president, it could see the Islamic Republic`s relations with the West thaw after 35 years in the deep freeze.
But there are powerful forces opposed, not least US President Barack Obama`s Republican opponents and Iran`s regional rivals Saudi Arabia and Israel, widely assumed to have nuclear weapons itself.
First the deal has to be done though.
"If the West gives up its excessive demands, we will certainly have a good deal in the nuclear negotiations with the P5+1," Iran`s First Vice President Es-Hagh Jahanguiri told Iranian media.
He was speaking as tens of thousands in Tehran marked the annual "Quds Day" in support of the Palestinians, shouting "Death to America" and "Death to Israel".
Iranian Foreign Minister Mohammad Javad Zarif, appearing on the balcony of the Coburg hotel where the talks were being held, appeared to be digging in for more talks, saying "it looks like" the negotiations will continue into the weekend.
Zarif late Thursday accused the West of "changes in the position and excessive demands."
Each of the nations in the group "have different positions which makes the task even harder," Zarif told the Iranian TV channel Al-Alam.
US Secretary of State John Kerry on Thursday warned the US would not be rushed into a deal, but insisted he would not stay in Vienna forever.
"If the tough decisions don`t get made, we are absolutely prepared to call an end to this process," Kerry told reporters.
Russian President Vladimir Putin said he believed a deal would be reached "soon".
"A compromise should be found," Putin said after hosting a summit of the Shanghai Cooperation Organisation in the Urals city of Ufa, where he met with President Rouhani on Thursday.
"In my opinion, it will be found soon," he said.The November 2013 interim accord saw Iran partially freeze its nuclear programme in exchange for minor sanctions relief.
Two deadlines last year to turn this into a lasting accord were missed but in April a framework accord was agreed in Lausanne, Switzerland, which negotiators are now trying to finalise.
Armies of technical and legal experts have made great strides working out the legal and technical nuts and bolts of what will be a fiendishly complex final agreement.
But they have got bogged down working out how exactly the deal will be implemented, including a timetable for dovetailing the lifting of sanctions with dismantling Iran`s nuclear programme.
Another major problem is Iran`s push to have a UN arms embargo lifted, something which appears to have driven a wedge between the Western powers on one side and China and Russia on the other.
"If the remaining gaps are not bridged by the end of this weekend, a break might prove inevitable," International Crisis Group analyst Ali Vaez told AFP.
"But leaving Vienna empty handed is more likely to stiffen the parties` positions than to soften them," he said.