The secretary of Iran's Supreme National Security Council has said Israel will be sorry if it continues to attack Syria's army and its allies.
Iran and Russia have both backed Bashar al-Assad in a seven-year war against rebels.
But Israel, increasingly concerned that its enemy Iran may establish a long-term military presence in its neighbour, says it has carried out more than 200 attacks against Iranian targets in Syria in the last two years.
"The Zionist regime has been trying to establish a crisis in Syria and has taken steps to directly support terrorist groups and target the Syrian army and forces who are confronting terrorism," Ali Shamkhani, secretary of Iran's Supreme National Security Council, said on Thursday, according to the semi-official Tasnim news agency.
"And if it continues, it will face reactions that will cause regret." He did not specify what this might mean.
The Supreme National Security Council, chaired by President Hassan Rouhani, decides on Iran's foreign and security policy together with Supreme Leader Ayatollah Ali Khamenei.
Shamkhani made the comments during a meeting with his Russian counterpart, Nikolai Patrushev, in Tehran.
Russia said on Monday it would supply Syria with an S-300 surface-to-air missile system despite strong Israeli objections, a week after Moscow accused Israel of indirectly causing the downing of a Russian military jet by Syria air defences.
