There are reportedly about 8 unresolved issues in Iran nuclear talks as deadline looms
"We are continuing to negotiate for the next couple of days. This does not mean we are extending our deadline," Mogherini told reporters.
The deal under discussion between Iran, Britain, China, France, Germany, Russia and the United States is aimed at curbing Tehran's most sensitive nuclear work for a decade or more, in exchange for relief from sanctions that have slashed Iran's oil exports and crippled its economy.
Russian Foreign Minister Sergei Lavrov said on Tuesday that around eight issues remained to be "finalised" before a nuclear deal between Iran and six powers is reached, Interfax news agency reported.
"We might see some ministers leaving in the next hours and then ready to come back," Mogherini said.
"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, adding that there remained several difficult issues to resolve.
The negotiators missed a June 30 deadline for a final agreement and then gave themselves until Tuesday.
(Reporting by John Irish, Louis Charbonneau, Arshad Mohammed and Parisa Hafezi)