Tear gas and water cannon have been deployed to control the crowd.
Lebanese security forces fired tear gas and water canons at protesters near the US embassy during the demonstration, TV footage showed.
Scuffles between protesters and police had already taken place by 10:30 a.m., and several injured people had been carried away from the scene by fellow demonstrators.
Some protesters also torched an effigy of Trump.More news: Border arrests plunge, deportation arrests soar — APNewsBreak
Lebanese Communist Party head Hanna Gharib addressed the demonstrators, calling the U.S. "the enemy of Palestine".
The U.S. Embassy in Beirut issued a security message reminding U.S. citizens of "the need for caution and awareness of personal security".
NPR's Ruth Sherlock reports from the demonstration that for the most part, the protesters were peaceful.
Protesters told CNN they condemned Trump's steps on Jerusalem's status and said they were angry at the "impotence" of Arab leaders in the wake of the controversial decision. US Embassy Beirut reminds US citizens of the need for caution and awareness of personal security.More news: U.S. court refuses to free convicted man featured in 'Making a Murderer'
LEBANESE security forces fired tear gas and water cannons at demonstrators near the USA embassy as they protested Washington's decision to recognise Jerusalem as the capital of Israel. One American flag was burned.
It warned that attempts to change the legal status of Jerusalem or to "change the Arab identity of the city" are "provocations to the feelings of Muslims and Christians across the Muslim and Arab world" and violates worldwide law. Since Wednesday evening, massive protests have been held throughout the Middle East, as well as in Asia and Europe.
Israel has laid claim to the entire Jerusalem being its capital, while Palestinians want East Jerusalem to be the capital of a future independent state. Political work is responsible work", said Arab League chief Ahmed Aboul-Gheit. "Jerusalem has been occupied for 50 years.
If Washington vetoes the resolution, the Arab ministers will ask for a similar resolution in the UN General Assembly, Palestinian Foreign Minister Riyad Al-Maliki said.More news: Indianapolis Colts vs Buffalo Bills
Palestinian Authority Foreign Minister Riyad Al-Malki called Trump's decision "illegal and illegitimate and null and void legally and politically", saying there would be no formal communication with United States officials.
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