VIENNA -- US Secretary of State John Kerry will hold in-depth discussions Monday with Iran's top diplomat in a bid to advance faltering nuclear negotiations, with a deadline just days away for a comprehensive agreement.

The scheduled talks come a day after Kerry and the foreign ministers of Britain, France and Germany failed to reach a breakthrough on uranium enrichment and other issues standing in the way of a deal that would curb Iran's nuclear program in exchange for the end of sanctions on Tehran.

Each of the top officials met with Iranian Foreign Minister Mohammed Javad Zarif (Moh-hahm-AD Jah-VAHD Zah-REEF). Russia and China sent officials to Austria's capital for this week's gathering.

The six world powers and Tehran will need to continue negotiations until July 20 and could decide to extend those talks past that informal deadline for a deal.

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