Quds Day was launched by Ayatollah Ruhollah Khomeini, the leader of Iran's 1979 revolution, and is held on the last Friday of the Muslim month of fasting Ramadan.
Thousands of Iranians rallied Friday to mark Quds, or Jerusalem Day, which will see demonstrations across the Mideast as the Trump administration tries to offer an Israeli-Palestinian peace plan.
The annual protests, also being held in Iraq, Lebanon and elsewhere, come on the last Friday of the Muslim holy fasting month of Ramadan.
Iran has marked Quds Day since the start of its 1979 Iranian Revolution by the late Ayatollah Ruhollah Khomeini. Al Quds is the Arabic name for Jerusalem, and Iran says the day is an occasion to express support for the Palestinians.
Israel views Iran as its archenemy in the Mideast. Iran does not recognise Israel and supports the militant groups Hamas and Hezbollah.
Rallies in 950 cities, towns
In Tehran, rallies began across the Iranian capital. They'll all head to Tehran University, where the ceremony will end at Friday noontime prayers. Similar rallies took place in 950 cities and towns across the country.
Tens of thousands of Iranians marking the annual "Quds (Jerusalem) Day" condemned a planned Middle East peace plan touted by US President Donald Trump as the "deal of the century."
State television said state-sponsored marches were being held in 950 communities across Iran and showed demonstrators carrying banners with slogans such as "Jerusalem is the eternal capital of Palestine" and "Death to America".
"No to the deal of the century" read a banner splashed across the news screen on state TV, which also showed a Quds Day march in neighbouring Iraq's capital Baghdad.
Mideast peace plan
This year's protests come as the White House is promoting the June 25 to 26 meeting in the Gulf state of Bahrain as the first phase of its long-awaited Mideast peace plan. That plan, whose specifics have yet to be released, includes large-scale investment and infrastructure work in the Palestinian territories, much of it funded by wealthy Arab countries.
Palestinian leaders say they won't attend the summit. American officials say the Bahrain conference will not include the core political issues of the conflict: borders of a Palestinian state, the status of Jerusalem, the fate of Palestinian refugees or Israeli security demands.
On Wednesday, Iran's Supreme Leader Ayatollah Ali Khamenei said that the US and its allies will fail to impose the so-called "Deal of the Century" on Palestinians.
Meanwhile, Iran's Foreign Minister Mohammad Javad Zarif has described the peace plan as "shameful."