"It is an act against Muslim unity, they must return from this path and make up for this big mistake," said Iran's supreme leader Ali Khamenei.
Arab nations that normalised ties with Israel last year have "sinned" and should reverse such moves, urged Iran's supreme leader Ali Khamenei.
"Some governments have unfortunately made errors -- have made big errors and have sinned in normalising (their relations) with the usurping and oppressive Zionist regime," Khamenei said on Sunday, referring to Israel.
"It is an act against Muslim unity, they must return from this path and make up for this big mistake," Khamenei added, in a speech marking a public holiday honouring the birth of the Prophet Mohammed.
Iran has in the four decades since the 1979 revolution positioned itself as a strong defender of the Palestinian cause.
"If the unity of Muslims is achieved, the Palestinian question would definitely be resolved in the best fashion," Khamenei said.
Shortly after Khamenei's speech, Iran's top security official, Ali Shamkhani, vowed to inflict many "billions of dollars" worth of damage in a "shocking response" if Israel strikes Tehran's nuclear programme.
The tweet by the secretary of Iran's Supreme National Security Council came in response to Israeli media reports that $1.5 billion (five billion shekels) had been approved to prepare the military for a potential strike on Iran's nuclear programme.
The United Arab Emirates, Bahrain, Sudan and Morocco all agreed to normalise ties with Israel in 2020, as Washington under the administration of then US president Donald Trump made Arab-Israeli rapprochement a foreign policy priority.
Egypt and Jordan were until last year the only two Arab countries to normalise relations with Israel.