“Deal of the century is not even the deal of a moment or a second,” Qassemi said in a post on his Twitter account.
“The world and the human history have seen many of such inept lunatics and such ‘null’ deals,” the ambassador added.
The diplomat, who was formerly an Iranian Foreign Ministry spokesman, further emphasized that at the end, (the Palestinian) nation will emerge victorious.
On Tuesday night, US President Donald Trump unveiled his long-delayed Middle East plan, a proposal Palestinian leaders called a "conspiracy" that "will not pass".
Following Trump's announcement, Palestinian President Mahmoud Abbas said "a thousand no's" to the plan.
The American plan has sparked widespread international condemnation.
The deal of century ploy, fronted by US President Donald Trump's son-in-law Jared Kushner, has already been rejected by the Palestinians, who say the White House's policies have been blatantly biased in favor of Israel.
Palestinians have cut off all contacts with the Trump administration since the US president broke with decades of bipartisan policy to recognize Jerusalem al-Quds as the capital of Israel in December 2017.
In June 2018, Leader of the Islamic Revolution Ayatollah Seyed Ali Khamenei reiterated the need for a referendum among “true Palestinians of all faiths,” being Muslims, Christians or Jews, adding that such a move would lead to the establishment of the Palestinian government.
Ayatollah Khamenei said the referendum and the subsequent formation of such a governing system would eventually translate into the destruction of the "bogus regime" of Israel in the not-too-distant future.