Tehran was first invited to participate in talks that began in Vienna late last month. There, the US and its allies attempted to formulate a compromise in which Iran would concede to Syrian President Bashar al-Assad eventually stepping down as part of a political solution to the more than four year civil war.

Delegates from the Iranian Foreign Ministry swiftly rejected any such compromise, and in the following days representatives of the Iranian Revolutionary Guard Corps aggressively reiterated that Iran would continue to fight to preserve the Assad regime, and would not consider any alternative to its rule.

By many accounts, this uncooperative attitude is consistent with the Iranian government’s recent upsurge in anti-American rhetoric and its general commitment to a hardline foreign policy. Some supporters of last summer’s nuclear agreement between Iran and six world powers expected that the diplomatic process would give way to a change in Iranian behavior, but others have been quick to conclude that such a change is not in the offing.

The Associated Press reported on Monday that US Vice Admiral Kevin Donegan, the commander of the US Navy’s Fifth Fleet, had expressed the view that Iranian behavior in the broader Middle East had not changed, but was continuing to destabilize the region. Donegan spoke positively about the nuclear agreement itself but kept it separate from a range of other Iranian activities that still represented cause for concern among American military leaders and policymakers.

Donegan specifically pointed to Iranian attempts to smuggle weapons to Shiite rebels in Yemen. He indicated that these efforts went beyond the single high-profile incident in which an Iranian vessel attempted to evade a US-led blockade, leading the two countries unusually close to violent confrontation.

He also indicated that Iran had been demonstrating general hostile behavior on a recurring basis, as by shadowing foreign vessels. “They like to show that they can shoot weapons when they’re in proximity,” Donegan explained.

The naval commander also suggested that the US would not be backing down from such aggression, either in direct response or as a general matter of policy. He said that notwithstanding the temporary absence of a US aircraft carrier in the Persian Gulf, US forces would continue to exert a strong presence in the region. But critics of the Obama administration may be inclined to question the reliability of these claims. Indeed, some see the mere willingness to negotiate with Iran over Syria as an indication that the US is giving Iran too much room to maneuver freely in the area.

Iran’s consistent refusal to cooperate or compromise in the previous Syrian security conference may raise some question about the motives for its return to the forthcoming session, which is set to begin in Vienna on Thursday. Iranian officials have said that they are waiting for foreign powers to adopt what Tehran has termed a “realistic” approach to the crisis, suggesting that the regime may believe it can pressure the US and its allies to allow Assad to stay.

But there are also other ways of interpreting Tehran’s continued presence at the negotiating table. According to Xinhua News Agency, Iranian Deputy Foreign Minister Hossein Amir-Abdollahian first acknowledged Iran’s continued participation in a telephone conversation with a representative of Russian President Vladimir Putin. This may provide a clue to Iran’s focus on the talks.

Thus far, Russia has supported Iran in its support of Assad, but several analysts have suggested that Russia’s position on this issue may not be as firm as Iran’s. IRGC commander Mohammad Ali Jafari expressed the same view last week, suggesting that it may be a long-term threat to Iran’s strategy. In the midst of these comments, evidence has accumulated to further suggest that Moscow might be more willing than Tehran to compromise with the West.

On Monday, the New York Times reported that Russian officials had declared a closely watched military trade contract to be in effect. On its surface, this apparent promise of imminent delivery of the advanced S-300 missile defense system suggests close collaboration between Iran and Russia. But it is not the first time that Russia has teased that delivery in the past few months. This leads the Times to speculate that the Russian statements are primarily aimed at forestalling an Iranian lawsuit over the contract, while delaying its actual execution.

In effect, by leaving the arms transfer in limbo, Moscow is leaving itself with leverage over both the West and Iran. This may in turn leave the door open for the Russians to be swayed either to compromise over the Syrian Civil War, or to recommitment to its support of the Assad regime. Iran’s continued presence at the Vienna security conference may thus be aimed at keeping tabs on the Russian position, so as to be prepared to react if it loses the Russian support that has allowed Iran to deepen its involvement in Syria over the past several weeks.