President Hassan Rouhani and other top officials attended a repatriation ceremony for the 104 pilgrims, who were among at least 464 Iranians killed in the September 24 crush.
"If it were proved that some (authorities) were guilty in this accident, we will not forgive" the loss of our loved ones, said a sombre Rouhani said, flanked by the heads of the judiciary and parliament as well as the chief of staff of supreme leader Ayatollah Ali Khamenei's office.
"If needed, the language of authority will also be used."
Rouhani called for a "fact-finding commission" into the disaster that Iranian leaders have blamed on Saudi "mismanagement and incompetence".
More From This Section
"All Islamic countries must learn why this tragedy happened," he said.
Saudi authorities have yet to provide a breakdown of the nationalities of the 769 Muslim pilgrims they say were killed, but many countries have announced the deaths of citizens.
Tallies of the dead from foreign officials and media from 24 countries put the toll at 1,036, well in excess of the Saudi figure.