"I cannot make any predictions on how much longer it will take" before all anti-Tehran sanctions are lifted, Fischer told Iran's state television news agency IRIB on Monday.
"But I hope that all sides will remain committed to the nuclear deal so that all of Iran's sanctions are lifted in due and scheduled time," he added as cited by AFP.
Fischer, speaking ahead of a two-day state visit to Austria by Iranian President Hassan Rouhani that begins on Wednesday, said the process of lifting sanctions on Iran had started, adding Austria alone cannot lift the sanctions.
Earlier, Iranian President's Chief of Staff Mohammad Nahavandian announced that president Rouhani will travel to Austria and Belgium in late March.
The visits will come after President Rouhani’s landmark trip to Europe, only days after a lasting nuclear deal between Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) came into force on January 16.
After visiting top Italian officials in Rome and the Pope in the Vatican City, the Iranian president headed to Paris, where he received a warm welcome from President Francois Hollande.