Ali Larijani led a 45-member Iran delegation to a summit of Muslim parliaments after the Islamic Republic was told the UAE would withdraw a proposal to set up a conflict resolution committee between Muslim nations.
Mr Larijani, the speaker of parliament, delivered a fiery address in which he repeatedly blamed the West, particularly the US and Israel, for plotting against the Muslim world and said Iran had evidence that Israel had orchestrated the assassination of Iranian nuclear scientists.
He also continued a campaign of vilification against the Special Tribunal for Lebanon (STL), which is investigating the murder of former Lebanese premier Rafik Hariri.
"Authoritarian governments have been busy for many years, planting discord among the Islamic ummah," he said. "We must not make room for the Americans and Zionists to play around with the fate of the Islamic ummah."
He reeled off a list of grievances against Western powers, saying they were destroying Jerusalem's Islamic features and were forcing Palestinians to immigrate from their lands, in addition to maintaining the siege of Gaza.