text: On Sunday, the Revolutionary Guard in Tehran held a funeral for two of its men killed in action in Syria, the latest of dozens in recent weeks.
  Revolutionary Guard commanders say they are defending their own country by fighting in Syria against the kind of terrorism that may eventually reach the streets of Tehran.
  Iran's support for the beleaguered Syrian President, Bashar al-Assad, has been costly in both blood and treasure.
  So when the invitation came from the US to join a push for establishing a new political process with the aim of ending the war in Syria, Iran was happy to accept.
  The invitation to Iran, which until recently was regarded by the US and its allies as part of the problem in Syria, could not have come without the nuclear deal reached in July.
  Nearly two years of direct nuclear talks led to an understanding that there were regional issues both nations had a strong interest in resolving.
  A telephone call from US President Barack Obama to King Salman succeeded in persuading Saudi Arabia to drop its objection to Iran's participation - for now.
  On Friday, for the first time in four and a half years of civil war in Syria, many of the main actors were at the table.
  EU foreign policy chief Federica Mogherini called it a historic meeting.
  Tehran's involvement in the talks on Syria alarmed Iranian hardliners.
  They fear the nuclear agreement may have opened the floodgates to undesirable Western influences, and they see Iran's participation in the talks as another worrying sign President Hassan Rouhani is deviating from the Islamic revolutionary path.
  It comes only weeks after the Supreme Leader, Ayatollah Ali Khamenei, himself a hardliner, had declared there would be no negotiations with the US on any issue.
  Furthermore, the hardliners discovered to their consternation the Syria talks involving top Western powers, Russia, China, Syria's neighbours, Saudi Arabia, Qatar and Egypt had made modest progress.
  All participants, including Iran, agreed to push forward with a political process that would:
  For Iran's hardliners, even this most general outline of a possible political process is a step too far.
  They criticised Foreign Minister Zarif for giving too much away and accused him of forgetting about what they regard as the central issue - the need to fight armed groups the West portrays as moderate forces.
  "We did not sell out the political future of Syria at the talks," countered Hossein Amir-Abdolahian, Deputy Foreign Minister, who is Iran's point man on regional policies.
  What the negotiators agreed to disagree on in Vienna, however, was the position of President Assad.
  Some wanted him gone soon after a ceasefire, but Iran is adamant he should stay until elections at the end of any transitional process.
  "It's the people of Syria who can decide on this," said Mr Zarif.
  Iraq and Syria are Iran's only allies in the Arab world.
  Syria provides Iran with vital access to southern Lebanon, where Iran is deeply committed to the Shia population and Hezbollah.
  Iran's policy of ensuring the survival of President Assad has many critics at home in Tehran who argue his position is no longer tenable after he has been responsible for so much bloodshed.
  New talks on Syria between the world powers are due in two weeks.
  But in spite of the uneasiness at home, Tehran is not about to abandon President Assad, because it fears any new regime in Syria may not be as accommodating to Iran.
  In Iran's calculation, it is vital that its ally Russia continues to back President Assad.
  So as long as Russia remains on side, the Iranian hardliners need not worry about a change in direction from Tehran.
  That is why many around the table in Vienna suspected Iran of engaging in the talks in order to find a solution that saves Mr Assad.
  Where key players stand on Assad
  If not Assad, then who?
  Iran's growing role
target: Coffins are being flown back to Tehran from Syria at an alarming rate.