In an interview with CBS's "60 Minutes" program, Kerry said on Sunday that the stated desire by Iranian President Hassan Rouhani for an agreement within three to six months could be met sooner if certain conditions are met.

"It's possible to have a deal sooner than that -- depending on how forthcoming -- and clear Iran is prepared to be," Kerry said.

"We need to have a good deal here. And a good deal means that it is absolutely accountable, failsafe in its measures to make certain this is a peaceful program”.

"If it is a peaceful program, and we can all see that -- the whole world sees that -- the relationship with Iran can change dramatically for the better and it can change fast," Kerry added.

Kerry's comments came amid a marked improvement in relations between Washington and Tehran in recent months that culminated in a landmark telephone conversation between Rouhani and US President Barack Obama on Friday.

The nascent rapprochement has raised the prospect of an agreement being reached about Iran's nuclear program which Tehran has long insisted is aimed at producing electricity for future of its more than 70-million population. 

On Sunday Iranian Foreign Minister Mohammad Javad Zarif told American ABC channel that “Iran is prepared to start negotiating.... We are willing to engage in negotiations. Of course the United States also needs to do certain things very rapidly”.

The Iranian foreign minister added that the resolution of Iran’s nuclear issue “will be a first step, a necessary first step, towards removing the tensions and doubts and misgivings that the two sides have had about each other for the last 30-some years.”

SHI/SHI