Iran, world powers miss second deadline to strike final deal

European Union foreign policy chief Federica Mogherini arrives for a press briefing outside Palais Coburg, the venue for nuclear talks in Vienna, Austria, July 7, 2015. Iran and major powers will continue negotiations on an historic nuclear deal past a deadline for a long-term agreement, which is set to expire later on Tuesday, Mogherini said. [Photo/Agencies]

VIENNA - Iran and six world powers missed their second self-imposed deadline to strike a final deal on Iran's nuclear issue on Tuesday, leaving the real deadline of the deal unknown.

Talks between Iran and major powers on Iran's nuclear issue will continue after Tuesday for a "couple of days", while the negotiations entered the most difficult and sensitive part of the talks, European Union foreign policy chief Federica Mogherini told reporters on Tuesday in Vienna.

The remarks of Mogherini came when several foreign ministers from six world major countries are finishing their meetings with their Iranian counterpart in the ongoing Iranian nuclear talks in the capital city of Vienna.

She said the deadline of the talks could be treated in a flexible way to give the negotiators more time to finalize the deal.

While Russian Foreign Minister Sergei Lavrov said there will be no artificial deadlines set for the ongoing nuclear talks, media reports from the United States suggested that an interim nuclear agreement between Iran and six major powers will be extended through Friday to provide more time for talks on a final agreement.

On the US side, negotiators are "more concerned about the quality of the deal than about the clock", said US State Department spokeswoman Marie Harf on her twitter account.

"We've made substantial progress in every area, but this work is highly technical and high stakes for all of the countries involved," said Harf.