A U.S.-led military attack on Syria will inevitably cause collateral damage, and one casualty could be rising optimism for rapprochement between Tehran and Washington.
President Hassan Rohani's election victory in July was widely seen as an opening for improved relations between Iran and the United States. Rohani took a relatively moderate position on policy issues during his campaign, pledging to improve ties with the West and try a different approach in negotiations over Iran's contentious nuclear program.
That was welcomed by Iranian voters
keen on seeing international economic sanctions lifted, and by many U.S. lawmakers open to talks that could prevent Iran from developing nuclear weapons.
Patrick Clawson, director of research at the Washington Institute for Near East Policy, says a U.S. intervention in Syria would considerably complicate such efforts.
"A military strike is likely to highlight the serious differences between the United States and Iran about developments in Syria," Clawson says. "That is more likely than not to complicate matters for reaching an agreement between the United States and its international partners with Iran about the nuclear impasse."
In turn, Iran's continued backing of the Syrian government, its main regional ally, could abruptly end any talk of lifting economic sanctions. This is because military intervention in Syria would be retaliation to a toxic gas attack the West believes was carried out by Syrian President Bashar al-Assad's forces.
"It would be very difficult for the United States to agree to a lifting of sanctions on Iran if Iran is perceived as providing vital support to a regime that uses chemical weapons," Clawson says.
The Iranian leadership has denounced possible military action against the Assad government, which is also a lifeline for the militant Shi'ite group Hizballah, Iran's proxy in neighboring Lebanon.
"U.S. intervention will be a disaster for the region," Supreme Leader Ayatollah Ali Khamenei said in addressing Rohani's cabinet on August 28, according to state television. "The region is like a powder keg; its future cannot be predicted."
Any fallout from U.S. military action in Syria would depend on the extent of the intervention, Clawson says. The repercussions of surgical strikes against specific regime targets will complicate matters less than an ongoing U.S. campaign to oust Assad.
Rohani has taken a more cautious approach. He has condemned the use of chemical weapons in Syria, without placing blame
, while joining Russian President Vladimir Putin in an August 28 telephone call stressed the need for a peaceful resolution to the crisis.
But in keeping with Iran's hard-line position, General Masoud Jazayeri, deputy in chief of Iran's armed forces, on August 26 warned that any U.S. intervention in Syria would be a "red line."
"The U.S. is aware of the limit of a red line in the Syrian front, and any crossing of the Syrian red line will have severe consequences for the White House," he was quoted as saying by Iran's Tasnim news agency.
Many observers doubt that such consequences would include military retaliation by Iran. The issue of chemical weapons hits close to home in Iran, who had forces and civilians gassed during the 1980-88 Iran-Iraq War, and the thinking is that Tehran would not respond with force to a brief and targeted strike.
But any military action would strengthen the position of Iran's hard-liners, who oppose talks with the United States and could drown out voices of moderation within Iran if Syria is attacked.
In order to protect its interests in Syria, Iran's leadership could opt to step up clandestine efforts in Syria by creating new proxies or calling upon existing groups such as Hizballah to fight for its interests.
"I would make it very difficult for him to call for greater relations with the West in the short term," Ghanem Nuseibeh, founder of the London-based political risk-analysis group Cornerstone Global Associates, says of the immediate political impact for Rohani.
"One of his main mandates, as far as international policy is concerned, becomes undermined as a result of really not being able to sell to the hard-liners in the government the importance of greater or closer relations with the West."