When Turkey voted against additional United Nations sanctions on Iran last May, it seemed the relationship between Ankara and Tehran was stronger than ever. But Turkey's growing political and economic influence in the Middle East may be gradually pushing Iran to the political sidelines.
Turkey and Iran share a 500-kilometer border; they enjoy $7.5 billion-worth of annual trade and one million Iranians visit Turkey each year.
But, last April, when Turkish President Abdullah Gul hosted a forum on Afghanistan with his Pakistani and Afghan counterparts, Iran was among the few participating countries not to send a representative at the Presidential level.
Elliot Hen-Tov, a scholar of Turkish-Iranian relations, thinks he knows why.
"Iran is not completely comfortable with Turkey," said Elliot Hen-Tov. "It never will be."
Hen-Tov says Iranian leaders are perplexed - even envious - that a country that was half as rich as Iran was years 30 ago, when the Islamic Revolution took place, is today twice as wealthy as the Islamic Republic.
"To see a neighbor that really was a backwater, an underdeveloped authoritarian country now emerge as a model, as a leader, must be very frustrating," he said. "And that impacts political relations at some point. Accepting Turkish leadership is just one step too far."
In recent years, the political dynamic between Ankara and Tehran has been turned completely on its head.
Today, Turkey is a major political and economic force in the Middle East. It's the 16th largest economy in the world and Iran looks to Ankara for economic benefits and cooperation.
Turkey has arbitrated an Israel-Syrian conflict; played a role in the political reconciliation of Lebanon; and is trying to bring together leaders of Syria and Saudi Arabia.
But by pursuing its current foreign policy strategy, Turkey is also taking on Iran's mostly self-ascribed role as defender of the Muslim underdog.
Just last week, Ankara announced it is determined to develop an industrial zone in Palestinian territories despite opposition from Israel.
Last month's Israeli attack on a Turkish-led aid flotilla to Gaza only helped crystallize Turkey's role as the newest advocate for the Palestinians
"That role as the alleged defender of the "Mosta'Zaffin" - or the Oppressed - in the region and beyond, that is a role that Iran only partially fulfilled in the past," said Hen-Tov. 'It may have seen itself as the leader in its own Revolutionary discourse but it was basically the next best thing on the market….You now have a better alternative on the market. "
Analysts say the Arab street hopes the more liberal Islam of Sunni Turkey can lead to solutions for persistent regional conflicts.
The shift means Middle Eastern players are relying less on the Islamic Republic for political backing.
Last month, Hamas refused Iran's offer to provide an escort for their aid ship to Gaza following the flotilla attack, saying the Iranian assistance might only complicate the situation.
"Supporters of Iran or affiliates such as Hezbollah or Hamas, they quickly have picked up on the signal that Iranian influence is perhaps not as valuable as Turkish influence," he said.
Surveys from a well-regarded polling organization in the U.S. also show that nearly half of Palestinians and 60 per cent of Lebanese have an unfavorable view of Iran.
Similar surveys show that the public in countries with large Muslim populations - including Turkey - lack the confidence Iranian President Mahmoud Ahmadinejad can do the right thing regarding world affairs.
Iran may have mixed feelings about Turkey's rise but Ankara is firm in its resolve to prevent the likelihood of military action over its neighbor's nuclear program.
That shared interest between Ankara and Tehran may be ultimately the strongest bond between these two neighbors.
Turkish officials were in Washington last month to defend their government's no-vote in the latest round of U.N. sanctions against Tehran.
Namik Tan is Turkey's ambassador to the U.S:
"It will be Turkey that will be hit hardest by the sanctions or use of force," said Namik Tan. "If we are asked to bear the burden, we should also be given the chance to engage effective dialogue with Iran. We are right next to Iran, ladies and gentlemen, not 10,000 kilometers away, like yourselves living in this wonderful country."
Despite the envy Iranian leaders may feel towards Turkey's growing regional influence, Tehran continues to view Turkey as an overall positive force.
Iran, after all, is Turkey's second largest natural gas producer after Russia. And Turkey acts as a buffer on Iran's border from the encroachment of Western NATO powers and to some extent Israel.
But analysts like Hen-Tov say if Ankara's influence on the Muslim world completely overshadows Tehran's presence in the Arab street, Turkey's gain may eventually become Iran's loss.