Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei says the "deal of the century" which is to be unveiled by the US is a crime against humanity, urging "everyone" to help defeat it.

"The ploy of the 'deal of the century' which is being plotted by the oppressive America and its treasonous cohorts is a crime against human society, and not just the Palestinian nation," the Leader said Saturday in his annual Hajj message.

"We are inviting everyone to actively participate in defeating the enemy's ploy and deception and believe that with the power and strength from God, this and all other ploys of the imperialist front is doomed to failure vis-a-vis the efforts and faith of the resistance front," he added.

The "deal of the century", a backchannel plan to allegedly reach a peace settlement between Israel and the Palestinians, is reported to recognize Israeli occupation of Palestine in exchange for economic incentives. The plan has widely been rejected by the Palestinians.

Ayatollah Khamenei described Palestine as one of the most important issues of the Muslim world regardless of their sect, race, and language.

“The greatest injustice of the recent centuries has happened in Palestine. In this painful drama, all that a nation had—their land, homes, farms, belongings, dignity, and identity— has been confiscated," the Leader said.

“This nation, with God’s assistance, has not surrendered to defeat and has not given up and today, they are fighting evermore passionately and braver than yesterday, but the ultimate outcome requires assistance from all Muslims.”

Ayatollah Khamenei's message came as millions of Muslims poured onto the plain southeast of the holy city of Mecca to mark the Day of Arafat on the second day of the annual Hajj congregation.

The Leader said the pilgrimage presents an opportunity for oppressed Muslim nations to “spread awareness” and denounce oppression and the rule of “arrogant world powers”.

Every year, the Leader issues a message on the occasion, giving guidelines on the need to uphold the rite of Bara'ah or the "disavowal of the infidels" and unite Muslims around the key messages of Islam.

"The ritual of Bara’ah which means shunning all forms of cruelty, oppression, vulgarity and corruption of the tyrants of the time, and rising against bullying and extortion of the haughty of the eras, is one of the great advantages of Hajj, and an opportunity for the oppressed Muslim nations," the Leader said.

"Today, renouncing the front of shirk [polytheism] and kufr [disbelief] of the arrogant powers headed by America means rejecting the killing of the oppressed, and waging wars.

"It means condemning the centers of terrorism such as Daesh and the American Blackwater. It means the Islamic Ummah’s shouts at the infanticidal Zionist regime and its backers and sponsors," the Leader said.

The ritual of Bara'ah, Ayatollah Khamenei further said, is an opportunity to "condemn the warmongering of America and its associates in the sensitive West Asian and North African region where they have brought the pain and suffering of the nations to the breaking point and yet they bring grave tragedies on them each and every day".

"It means shunning racism, and discrimination based on geography, race, and color of skin. It means repudiating the arrogant and vicious behavior of aggressive and seditious powers vis-a-vis the dignified, noble and just behavior which Islam invites everyone to embrace."

Ayatollah Khamenei described the Hajj as a “model” demonstrating Islamic principles and uniting all Muslims together in worship of God.

Each and every able-bodied Muslim, male or female, is required to complete the religious trip to the holy city of Mecca at least once in their lifetime if they also have the sufficient financial capacity to do so.