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Iraqi Shi'ite cleric Moqtada al-Sadr delivers a sermon to worshippers during Friday prayers at the Kufa mosque near Najaf, Iraq Sept. 23, 2016. Reuters

One of President Donald Trump's major campaign promises involved moving the United States embassy in Israel from Tel Aviv to Jerusalem, something no president has ever done before. The plan was denounced by Palestinian President Mahmoud Abbas, but a prominent Iraqi cleric said Tuesday it could mean war.

"Transferring the U.S. embassy to Jerusalem would be a public and more explicit than ever declaration of war on Islam," said Moqtada al-Sadr in a statement.

Sadr, who once led a militia in the fight against U.S. forces in Iraq, called for the "immediate closure of the U.S. embassy in Iraq" if the transfer occurs. He also asked for the "formation of a special division to liberate Jerusalem."

It's unclear when, or if, the Trump administration will make the move happen. Nothing yet exists on the White House website on the subject.

"We are at the very beginning stages of even discussing this subject," said White House press secretary Sean Spicer Sunday.

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A Palestinian demonstrator holds a caricature of President Donald Trump during a protest against a promise by Trump to re-locate U.S. embassy to Jerusalem, in Rafah in the southern Gaza Strip Jan. 24, 2017. Reuters

Because both Israel and Palestine view Jerusalem as their capital, their respective leaders had vastly different reactions to Trump's proposed move.

"Any statement or position that disrupts or changes the status of Jerusalem is a red line, which we will not accept," said Palestinian President Mahmoud Abbas in a speech earlier in January.

Other U.S. officials, including former Secretary of State John Kerry, have come out against the move as well.

"We think it's ill-advised," he said.

Trump enjoys a friendly relationship with Israeli President Benjamin Netanyahu and has invited him to visit Washington in February. The White House announced the two leaders "agreed to continue to closely consult on a range of regional issues, including addressing the threats posed by Iran," in a statement after their phone call Sunday.

The U.S. has always had its embassy located in Tel Aviv and has never had an embassy in Jerusalem. Currently, 86 countries have embassies in Tel Aviv and none have embassies in Jerusalem.