Iran is in talks with the United States and five other big powers, Britain, China, France, Germany and the United States, on an agreement under which Tehran would curtail its nuclear programme in exchange for relief from economic sanctions.
The United States, Israel and some other nations suspect Iran is using a civilian nuclear energy programme as a cover to develop a nuclear weapons capability. Iran denies this, saying its programme is for peaceful purposes.
Making his second visit to Vienna in a week, Hammond played down expectations that an agreement was near at hand.
"The work goes on. You are going to see ministers coming and going to maintain the momentum of these discussions. I don't think we're at any kind of breakthrough moment yet and we will do whatever we need to do to keep the momentum," Hammond told reporters upon arrival in the Austrian capital.
Iran and the major powers missed Tuesday's deadline for a final agreement and gave themselves another week, until July 7, to try to work one out.
The foreign ministers of Britain, China, France and Germany will all be in Vienna on Thursday, joining US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif, who have been in intense negotiations.
Russia has not announced any plans for Foreign Minister Sergei Lavrov to join the talks on Thursday. Zarif has already returned to Tehran once since the current round of ministerial talks began on Saturday. There were suggestions, but no confirmation, that he might go back to the Iranian capital again later in the week.
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