In last-ditch efforts in search of a final agreement on the Islamic Republic's nuclear program, Iran and its negotiating partners had already extended their deadline for the talks to Tuesday.
Mogherini added the two sides are "working very hard to finalize an agreement," saying, "We are using the time we have in a flexible way."
"This does not mean we are extending our deadline. I told you one week ago more or less, we are interpreting in a flexible way our deadline, which means that we are taking the time, the days we still need, to finalize the agreement," she said.
The EU official emphasized that a comprehensive deal between Iran and the six world powers is "something which is still possible even if we are now getting into the difficult time. I am here to stay, to continue together with all the teams, all the six teams are here."
Mogherini said the P5+1 foreign ministers are likely to leave the Vienna talks but "are ready to come back in the coming hours and days."
P5+1 'lack of consensus' prolonging talks
An informed source close to Iran’s delegation also said “lack of consensus” among P5+1 countries and the six countries’ “inability to make a tough decision about the removal of sanctions” against Iran are among the main reasons for the continuation of the talks for several more days.
The source, whose name was not revealed, told IRNA that the P5+1 countries are now expected to prove their political will.
Meanwhile, US State Department spokeswoman also said the terms of the 2013 interim deal between Iran and the six powers have been extended until Friday as intensive talks continue.
"To allow for the additional time to negotiate, we are taking the necessary technical steps for the measures of the Joint Point of Action (the 2013 agreement) to remain in place through July 10," Marie Harf said.
Iran-P5+1 meeting
Iran and the P5+1 countries resumed their intensive talks on Tuesday in a bid to remove the remaining stumbling blocks to a final deal.
Iranian Foreign Minister Mohammad Javad Zarif and his counterparts from the P5+1 countries and Mogherini met for the third time in a day.
Speaking to reporters on Monday, White House spokesman Josh Earnest said:"I would say that it's certainly possible."
Following late Monday talks, foreign ministers of the five permanent members of the UN Security Council – the US, France, Britain, China and Russia – plus Germany met briefly on Tuesday without the presence of the Iranian negotiators.
Nuclear deal ready in few days: Russia
Russian Foreign Minister Sergei Lavrov said on Tuesday that Iran and the P5+1 countries have just days before they reach the final nuclear deal.
"It [final deal] is a very broad, very intense document and I think few days are left to wait before you can familiarize yourselves with it," Lavrov told reporters in Vienna.
He added that the negotiators "are not setting themselves any artificial deadlines… but they all focus on reaching quality agreements."
“And there is every reason to believe that we will achieve this," the Russian minister pointed out.
"I can assure you that there remains one major problem that's related to sanctions: this is the problem of an arms embargo," Lavrov said.