EU's top diplomat due at Iran talks Saturday

(BRUSSELS) - EU foreign policy chief Federica Mogherini is expected in the Swiss city of Lausanne on Saturday to take part in tough negotiations on Iran's contested nuclear programme, her office said.

"The High Representative and Vice-President Federica Mogherini will travel to Lausanne today, 28 March 2015, to meet ... foreign ministers and Iranian foreign minister Javad Zarif in the context of the ongoing nuclear talks," a statement said.

Mogherini had previously been expected at the talks on Sunday.

Six major powers are in tortuous negotiations with Iran to try and reach agreement on the contours of what they hope will be a historic deal by Tuesday.

Since a major diplomatic push to resolve the long-running crisis began in 2013, US Secretary of State John Kerry and Zarif have met several times, but have twice missed a deadline to nail down an accord.

The powers want Iran to shrink its nuclear programme in order to make it easy to detect any dash to make a bomb under the guise of its civilian atomic programme.

In return, Iran wants an easing of international sanctions that have excluded the Islamic republic from lucrative oil markets and crippled its economy.