The parties involved in Iran's nuclear talks packed up their bags after a week of talks in Laussanne, Switzerland.

They're deadlocked over sensitive atomic research and the lifting of sanctions, western officials say.

US Secretary of State John Kerry was en route to London where he'll meet with European counterparts.

He said the meetings were good but his London trip is meant to bridge differences that remain among the Americans and Europeans over details of the talks. 

Iranian Foreign Minister Mohammad Javad Zarif didn't stop to speak with reporters but expected a deal next week when talks resume. 

Technical experts from both sides have been meeting daily to discuss the various options of a deal.

Including Iran's atomic energy chief Ali Akbar Salehi who said progress made so far was "positive" in areas of mutual understanding.

While some headway was made over the past year, differences on major sticking points are still wide enough to potentially derail an agreement.

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