The protesters answered a call by Muslim groups for a peaceful march to carry supplies to residents of the Sunni town where dozens of Iraqis have been killed since US marines launched an offensive on Sunday against resistance fighters.
"Our families in Falluja, remember that our dead go to heaven and theirs to hell," read a banner held by the marchers who had gathered early on Thursday at the Um al-Qura mosque in west Baghdad where people donated food, drinks and medicine.
"No Sunni, no Shia, yes for Islamic unity. We are Sunni and Shia brothers and will never sell our country," they chanted.
The marchers carried Iraqi flags as well as portraits of Palestinian Shaikh Ahmad Yasin, the spiritual leader of Hamas killed last month by Israel, and Iraqi Shia cleric Muqtada al-Sadr, whose forces were fighting the US-led occupation.
Shaikh Ahmad Abd al-Ghafur al-Samarai, the imam and a member of the Committee of Religious Clerics, said: "Baghdad residents decided to send initially 90 cars with food and medicines to Falluja families."
"The people who are occupied have the right to fight occupation, whatever the means they use"
Shaikh Ahmad Abd al-Ghafur
imam, Um al-Qura mosque
The Iraqi Red Crescent got permission from occupation forces following negotiations over one day and one night to bring these supplies into the city, he said.
"We want to express solidarity with our brothers who are being bombed by warplanes and tanks. People donated these things, and women even sold their jewellery," he said.
"It is a form of jihad which can also come in the form of demonstrations, donations and fighting. The people who are occupied have the right to fight occupation, whatever the means they use," he said.
He called on the US army to stop the operation in the city.
"This only brings hatred and enmity. Americans killed 20 more people than those who are actually carrying arms. They killed the elderly praying at the mosques, as well as women and children. This is indiscriminate killing."
He condemned the mutilation of the bodies of four security workers slain in Falluja last week in an incident that sparked US outrage, but said US troops "are doing the same by mutilating the residential neighbourhoods".