Iranian President Hassan Rouhani blasted his US counterpart Donald Trump's plan to recognise Jerusalem as the Israeli capital on Wednesday, saying it would not be tolerated.
Rouhani also spoke with Turkish President Recep Tayyip Erdogan by phone, describing Trump's announcement as "wrong, illegitimate, provocative and very dangerous", according to an account posted on the Iranian government's website.
He also agreed to attend a special summit of the Organisation of Islamic Cooperation, the main pan-Islamic body, on December 13, which Erdogan called to discuss the issue.
Rouhani had earlier been speaking at an international conference in Tehran promoting Islamic unity and marking the anniversary of the birth of Islam's Prophet Mohammed.
Iran "will not tolerate a violation of Islamic sanctities," he said in reference to Trump's Jerusalem announcement.
"Muslims must stand united against this major plot."
Iran's supreme leader Ayatollah Ali Khamenei also spoke at the event, saying the US move was the result of "paralysis and incompetence".
"The Islamic world will undoubtedly stand against this plot and the Zionists will receive a big blow from this action and dear Palestine will be liberated," Khamenei said.
Since the 1979 Islamic revolution, Iran's opposition to Israel and support for the Palestinian cause has been central to its foreign policy.
The issue has again come to the fore in recent weeks amid rumours that regional rival Saudi Arabia has sought to build ties with Israel in order to better face down Iran's growing influence.
Iran was dedicated to building unity among Islamic countries, Khamenei said, but "unfortunately there are rulers and elites in this region that dance to the tune of the US: they do whatever the US desires against Islam."
His official Twitter account in English, which exists despite the messaging service being banned in Iran, later added: "We advise them: the outcome of what some states, in region, are doing will be as Quran says, 'their own destruction'".
The Iranian account of Rouhani's conversation with Erdogan quoted the Turkish president as saying: "Trump's insolence is a result of internal differences in the Islamic world".
"Now the Islamic world must demonstrate its unity and oppose this move," Erdogan reportedly said.