The two-time former president also warned that an international "consensus" had formed against Iran over its nuclear ambitions, in contrast with hardline President Mahmoud Ahmadinejad's claim that Tehran cannot be isolated.
"The most important thing needed inside is unity at a time that our country faces increased cruel resolutions, insults and bullying," Rafsanjani said. "The enemies will step up their evil-doing if they feel we do not have the same voice.
"A consensus appears to have formed against us, and the big powers have cooperated to deny our country's natural nuclear rights," he said, referring to a new UN nuclear watchdog resolution condemning Iran over its atomic work.
Rafsanjani, who heads Iran's top arbitration body, the Expediency Council, is close to Iran's opposition, which claims Ahmadinejad's June re-election was due to massive fraud.
The poll has bitterly divided Iran's political elite and dragged the country into one of its worst political crises as the defiant opposition continues to dispute the result and call for more protests.
Cracks in the unity of the regime became apparent during the autumn, after Ahmadinejad proposed shipping low-enriched uranium abroad, where it would be further refined and returned as fuel for a medical research reactor in Tehran.
Subsequent meetings with the International Atomic Energy Agency and key world powers led to a proposed deal under which Russia and France would have done the work.
But opposition quickly emerged among various factions of the governing elite, and Tehran ultimately rejected the deal.
In the end, Ahmadinejad announced on Wednesday that Iran would carry out the further enrichment itself.
Rafsanjani has been the target of attacks by Ahmadinejad and his hardline supporters over his ties with the opposition.
He said "the only one who can pave the way to unity is the supreme leader," Ayatollah Ali Khamenei, who has openly sided with Ahmadinejad and condemned the opposition over the street protests.
A pragmatic conservative, Rafsanjani has always been critical of Ahmadinejad's confrontational foreign policy and inflammatory rhetoric.
World powers have warned Iran could face a fourth set of UN sanctions after it vowed to increase its uranium enrichment capacity in reaction to an International Atomic Energy Agency resolution censuring it over such work.
"They need us more than we need them. It is psychological warfare and isolating Iran is impossible," Ahmadinejad said in a televised interview on Tuesday.
Another influential conservative cleric, Grand Ayatollah Nasser Makarem Shirazi, also called for an end to political squabbling, saying Iranians should "put aside their differences and unite more than ever."
Shirazi, whose remarks were carried in the press, also struck out at Russia and China, long considered more favourable to Iran than Western powers but who also voted in favour of the latest IAEA resolution.
He said that, rather than being friends of Iran, they were "seeking only their own interests."
