Iran, world powers push for nuclear deal as clock ticks towards deadline

European Union Political Director Helga Schmid (L), European Union High Representative Federica Mogherini (C) and Iranian Foreign Minister Javad Zarif wait with others for a meeting with officials from P5+1, the European Union and Iran at the Beau Rivage Palace Hotel in Lausanne March 31, 2015. REUTERS/Brendan Smialowski/Pool

LAUSANNE, Switzerland (Reuters) - With a deadline hours away, Iran and six world powers stepped up the pace on Tuesday in negotiations over a preliminary deal on curbing Tehran's nuclear programme while officials cautioned that any agreement would likely be fragile and incomplete.

For nearly a week, the United States, Britain, France, Germany, Russia and China have been trying to break an impasse in the talks, which are aimed at stopping Iran from gaining the capacity to develop a nuclear bomb in exchange for easing international sanctions that are crippling its economy.