TEHRAN — It was meant to be a crowning moment in which Iran put its own Islamic stamp on the Arab Spring. More than a thousand young activists were flown here earlier this week (at government expense) for a conference on “the Islamic Awakening,” Tehran’s effort to rebrand the popular Arab uprisings of the past year.

As delegates flooded into a vast auditorium next to a space needle in western Tehran, a screen showed images of the Iranian revolution in 1979, morphing seamlessly into footage of young Arab protesters in Tunisia, Egypt, Bahrain, Libya and Yemen.

But there was a catch. No one was invited from Syria, whose autocratic president, Bashar al-Assad, is a crucial Iranian ally. The Syrian protesters are routinely dismissed by Tehran’s government as foreign agents — despite the fact that they are Muslims fighting a secular (and brutal) dictatorship.

That inconvenient truth soon marred the whole script. As the conference began, a young man in the audience held up a sign with the word “SYRIA?” written in English. Applause burst out in the crowd, followed by boos. Audience members began chanting the slogan of the Syrian protesters: “God, freedom and Syria!” But they were drowned out by others chanting pro-Assad slogans.