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The meeting, a significant thaw in diplomatic relations between the countries, is designed to explore the support the Iranians can give to the fight against Islamic State (Isis) in Iraq and Syria. [...]

Cameron is expected to make clear that Isis is a common and extremely serious threat that can only be tackled in Iraq and that Iran must drop its support for President Assad, who, in the words of Downing Street, has "created the conditions that have allowed terrorism to flourish".

Cameron will also send a tough message to the Iranians on the long-running nuclear negotiations on behalf of the E3 + 3 group that: "Iran has a rare opportunity to embolden its prosperity through a deal but this is only possible if Iran is willing to show flexibility and be realistic about the future scope of its nuclear programme, in particular the issue of enrichment."

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