Iran foreign minister holds surprise talks with Turkey's Erdogan

Iranian Foreign Minister Mohammad Javad Zarif held previously unannounced talks on Wednesday with Turkish President Recep Tayyip Erdogan, with the situation in Syria likely dominating the agenda.

With expectations growing of an offensive by Tehran ally President Bashar al-Assad in Syria's Idlib province bordering Turkey, Zarif met with Erdogan for an hour at the ruling party headquarters in Ankara.

Turkish Foreign Minister Mevlut Cavusoglu, who attended the meeting, said "bilateral ties... [and] Syria" were on the agenda, state-run Anadolu news agency reported.

Zarif, who heads now to Pakistan, posted on Twitter after the meeting that the talks had been "fruitful".

Tehran supported Ankara as it was hit by sanctions from Washington, which have contributed to a sharp fall of the Turkish lira.

Turkey has kept a wary eye on the possibility of a Syrian government offensive in Idlib, where it has backed rebel factions and deployed its own troops.

Ankara has throughout the seven-year civil war in Syria supported rebels seeking to overthrow Assad, but has put differences aside to form a three-way alliance with Tehran and Moscow.

Erdogan and his counterparts Hassan Rouhani of Iran and Russia's Vladimir Putin are due to meet in Iran for a summit on Syria on 7 September, Turkish reports have said.

But analysts say that Idlib, which is largely controlled by rebel groups, may test the alliance with Turkey, as Ankara warns a military solution could lead to catastrophe and a new influx of refugees across its borders.

Turkey has 12 military observation posts inside Idlib aimed at monitoring a de-escalation zone and media reports have said it has sent concrete blocks over the border to reinforce them in case of an assault.

Russian Foreign Minister Sergei Lavrov on Wednesday called on the West not to stand in the way of an "anti-terror operation" in Idlib.

Lavrov also said there is "full political understanding" between Russia and Turkey, adding that it was necessary to "disassociate the so-called moderate opposition from terrorists".

The offensive would initially target southern and western parts of the rebel territory, but not yet Idlib city, an official in the regional alliance backing Assad told Reuters on Wednesday.

"The final touches for the first stage will be completed in the coming hours," the official who was not identified added, without saying when it would start.