TEHRAN (FNA)- Iranian Vice President and Head of the Department of Environment Masoumeh Ebtekar said the country's negotiating team are standing firm on Islamic Republic's redlines.

"The other side knows well how firm the Iranian team of negotiators is standing on its principles and redlines," Ebtekar told reporters on Friday.

She underlined that the Iranian negotiators will never withdraw from their stances, and said, "I hope that these negotiations will result in a good agreement."

Late on Thursday night, diplomatic sources in Vienna cautioned that the western powers have toughened their stances after the US lost a self-imposed deadline for a deal with Iran and are raising even more demands from the Iranian team.

The source said the western parties to the talks with Iran, specially the US, have in the last few days raised excessive demands beyond earlier agreements, making the road to a draft final nuclear deal even more bumpy.

The source said Iran is determined to clinch a deal and it has shown much flexibility on this path, but the US-led West has been raising excessive demands and shows "fading respect for its earlier agreements with Iran".

"They have started psychological operations and are playing the blame game to make Iran surrender to their increasing demands or wait to be portrayed as the party to blame for the potential failure of the talks," the diplomat added.

The source also strongly rejected the allegations made by certain western media outlets that the Iranian team is referring the opposite sides' proposals or the draft text to Tehran to ask for permission, reiterating that "the Iranian team of negotiators have been vested with full authority to strike a deal on behalf of the Islamic Republic of Iran based on the country's specified redlines, and does not need to refer anything to Tehran."

The diplomat strongly warned the western powers' approach in the last few days "is pushing the talks into a deadlock".

Earlier on Thursday night, Iranian Foreign Minister Mohammad Javad Zarif left a new post on his Twitter account, saying, "We're working hard, but not rushed, to get the job done. Mark my words; you can't change horses in the middle of a stream."

Minutes later, US Secretary of State John Kerry also appeared in front of the cameras in Vienna, and said, "Despite all the agreements we have made so far, some tough issues have remained unresolved."

"These issues should be resolved. And tough decisions should be made," he added, and continued, "We want a deal that stands the test of time."

Kerry said the negotiations are not open-ended, but he didn't say how long the talks would last.

By Fars News Agency