U.S. Secretary of State John Kerry says he is engaged in "very tough" negotiations in Vienna with Iranian counterpart Mohammad Javad Zarif over Iran's nuclear program.
Kerry's comments on July 14 come six days before a deadline for a deal curbing Iran's controversial nuclear program is to expire.
A U.S. official told RFE/RL's Radio Farda in Vienna that Kerry is ready to "take the time necessary to gauge Iran's willingness to reach a solution to the crisis" and "see if progress can be made."
But there are reports that Kerry will fly to Egypt on July 15 to seek help in getting a cease-fire in the Gaza Strip.
The foreign ministers of Britain, France, and Germany left Vienna after pressing Iran on July 13 to make key concessions.
Russia and China sent lower-level officials to the talks.
Britain's William Hague said that no "decisive breakthrough" was achieved and there remained a "huge gap" on the issue of uranium enrichment.
The six powers, which also include Russia and China, want Iran to dramatically reduce the scope of its enrichment program, while Tehran wants to expand it.
With just six days remaining until a July 20 deadline to strike a deal, the face-to-face meeting of Kerry and Zariff appears to be a measure of both sides' determination to negotiate.
The high-level meeting in Vienna is notable, as the United States and Iran have not had diplomatic relations for three decades.
Many experts believe that if Kerry fails to get Iran to give ground, he will recommend to U.S. President Barack Obama that the July 20 deadline be pushed back.
But Michael Mann, a spokesman for EU foreign-policy chief Catherine Ashton, told RFE/RL's Radio Farda correspondent Hannah Kaviani in Vienna on July 14 that, for now, there is no talk of extending the deadline:
"Our first objective is to try and overcome all the problems before then. I don't think I am going to get into speculating about extensions because the moment people start to think about extensions, there is always the danger that people take their foot off the gas pedal," Mann said. "Our aim still remains to get a deal by" July 20.
That deadline was set in an interim deal in November that saw Western powers lifting some sanctions on Iran in exchange for Iran freezing or reducing some of its nuclear activities.
Western powers are seeking an accord with Iran that would finally dispel their fears Tehran might develop nuclear weapons under the guise of its civilian program.
Iran, which says its nuclear program is purely for energy production, denies seeking an atomic bomb and wants the lifting of all UN and Western sanctions, which have crippled its economy.