The claims now that Iran's Syrian allies used similar tactics, including possibly unleashing sarin gas, has forced Tehran's leaders into perhaps their most difficult juncture of the nearly 30-month civil war. Iran's rulers could face an uncomfortable backlash at home — and possibly stir upheavals inside its powerful Revolutionary Guard — if they're seen as ignoring allegations and U.N. investigations into possible chemical attacks by Bashar Assad's regime.
Yet Iran remains, for the moment at least, solidly behind Assad and seeks to shift attention to efforts at blocking possible Western military action against Syria. Damascus is a critical ally for Tehran as a major foothold in the Arab world and its pathway to funnel aid to its main proxy militant, Hezbollah in Lebanon.
Iran's strategy includes a series of warnings that Israel could be drawn into a wider conflict — most likely by Hezbollah offensives — if the U.S. and others launch attacks on Syrian government sites. Iran's Supreme Leader Ayatollah Ali Khamenei earlier this week described possible Western attacks as "a spark in a gunpowder store."
Tehran also is using its diplomatic leverage with Russia and China to try to slow the momentum toward possible military action.
On Thursday, Iran's new president, Hasan Rouhani, called possible military strikes on Syria an "open violation" of international laws. The comments, reported by state TV, followed talks by telephone with Russian President Vladimir Putin.
Rouhani repeated his blanket condemnations of any use of chemical weapons. But he also tried to appeal to political blocs in the West, including the U.S., that are wary of a rush to military action.
"Early judgment can be dangerous," said Rouhani, insisting more time is needed to probe the allegations that it was Assad's regime that used possible chemical agents in an Aug. 21 attack that the aid group Doctors Without Borders says killed at least 355 people. Syrian officials insist that rebels carried out the attack.
Iran's seesaw strategy of denouncing chemical weapons but not directly implicating Assad appears to underscore the ongoing debates inside Iran's leadership of just how far to stick by Assad.
Last year, several current and former Iranian diplomats published opinion articles questioning whether Tehran should stick by Assad's regime or begin to weigh alternatives. Then in October — as the value of Iran's currency plunged — some merchants in Tehran's main bazaar chanted against the government's financial aid to Assad's regime.
The current quandary also pushes Rouhani's government into its first serious policy test. If U.N. findings conclude that Assad's military waged a chemical attack, Rouhani may have to make a calculation: Whether standing by Assad is worth the potential blow to his overall goals of building better ties with the West and trying to end the standoff over Tehran's nuclear program.
Such decisions cannot be made by Rouhani alone and must pass through Khamenei and the rest of the ruling establishment, including the Revolutionary Guard. But pressure could quickly mount to review Iran's backing for Assad in a country that has made the horrors of chemical attacks a centerpiece of its remembrances of the 1980-88 war with Iraq, which was then backed by Washington.
Iran estimates 100,000 Iranian soldiers and civilians were exposed to Iraqi chemical weapons, mostly mustard and nerve gases. Tens of thousands died on the battlefields from chemical exposure and thousands more suffered serious, and sometimes fatal, aftereffects such as skin lesions and chronic breathing problems.
"There seems to be deep division in the Iranian leadership as to what to do with Assad," said Meir Javedanfar, a lecturer in Iranian affairs at the Interdisciplinary Center in Herzliya, Israel. "The moderates seem to want to distance Iran from him as he is becoming a serious diplomatic and financial liability. The conservatives, headed by the Revolutionary Guard, seem to want to continue supporting him, because they see everything and anything to do with Syria as their turf."
The claims of chemical attacks by Assad's forces could "tip the balance," he said.
"The last thing Iran needs right now is to be seen as the co-sponsor of a regime which has carried out one of the biggest sectarian massacres in this region," said the Iranian-born Javedanfar.
U.N. inspectors investigating the alleged attack are expected to leave Syria on Saturday. Speaking in Vienna, U.N. Secretary-General Ban Ki-moon urged for the team to complete its work and issue findings before any decisions are made on possible military strikes.
This could leave Iran with more time do groundwork on two fronts: Stepping up the warnings against possible retaliatory attacks by the U.S. and allies, and trying to figure out Tehran's response if the U.N. points the finger at Assad.
Iran's foreign minister, Mohammad Javad Zarif, has started a speed-dial diplomacy effort with calls to at least 10 counterparts in Europe and the Arab world.
"In the current sensitive situation, preventing war is the best policy for Iran," said Heshmatollah Falahatpisheh, a former lawmaker and currently a Tehran-based political analyst. "Iran can do that through lobbying with Russia, Western countries and indirect lobbying with the U.S."
This mostly takes the form of dire warnings that the region could further unravel if Western militaries directly act to cripple the Assad regime — as they did in Libya in 2011 to allow rebel factions to turn the tide against Moammar Gadhafi's forces.
Hossein Sheikholeslam, Iran's former ambassador to Damascus, told Iranian state TV that Western military attacks against Syria will lead to an "extensive explosion of events in the region."
Already, the Syrian civil war has brought serious spillover. Western governments are deeply worried over the rising profile of Islamists, foreign jihadi fighters and al-Qaida-inspired militias among the rebels. Lebanon's Shiite Hezbollah militant group has intervened to fight on the side of Assad, angering Arab Gulf states.
An editorial in the hardline Kayhan newspaper by Hossein Shariatmadari, an adviser to Khamenei, urged Syria to consider "possibilities and targets" such as Gulf states and neighboring Israel and Turkey as part of its "legitimate defense" in case of Western attacks. In the southwestern province of Khuzestan, another Khamenei aide, Ayatollah Mohammad Ali Jazayeri, urged for "soldiers of Islam" to support Syria if it came under Western attack.
But Iran's political leadership has given more nuanced signals, including speculation they could reassess their relations with Assad if the chemical allegations are conclusively backed by the U.N. team.
"Iran, as a major victim of chemical weapons, is a pioneer in fighting any kind of inhuman weapons across the world," said Rouhani at a Cabinet meeting Wednesday. "Iran strongly condemns any use of this weapon."
Associated Press writer Nasser Karimi in Tehran contributed to this report.
Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.