[caption id="attachment_153256" align="alignright" width="224"] U.S. Secretary of State John Kerry, Britain's Foreign Secretary Philip Hammond, Russian Foreign Minister Sergei Lavrov, Iranian Foreign Minister Javad Zarif, German Foreign Minister Frank-Walter Steinmeier, French Foreign Minister Laurent Fabius, EU High Representative Catherine Ashton, Chinese Foreign Minister Wang Yi (L-R) pose for a family picture during their meeting in Vienna November 24, 2014. (Reuters)[/caption]

(Reuters) - Iran nuclear talks have made progress, but some very difficult issues remain and it is hard to tell if there can be a breakthrough when negotiations resume next week, a senior European diplomat said on Friday.

Six world powers have given themselves an end-June deadline to reach an agreement that curbs sensitive Iranian nuclear work in exchange for sanctions relief. The Western powers hope to have a political framework agreement by the end of March.

U.S. Secretary of State John Kerry will travel to Lausanne, Switzerland, on March 15 for the next round of talks with Iran.

The senior European diplomat, speaking to journalists on condition of anonymity, said: "We've really made progress, particularly in the last weeks, but there are still some very difficult issues." It was impossible to tell if next week's talks would produce a breakthrough, the diplomat added.

By Reuters