The demonstrators also protested against the presence of US military bases in the region.
"
The American is a coloniser who has come to cause destruction
"
Demonstrators
Bahrain, a key Washington ally in the Gulf, is home to the American Fifth fleet, and hosts about 1,000 US military personnel.
The United States and Britain have massed troops and equipment in the region, ahead of a possible campaign over Iraq's alleged weapons of mass destruction.
Opposition leaders, parliamentarians and human rights activists took part in Friday's peaceful march in the Bahraini capital, Manama.
"The American is a coloniser who has come to cause destruction," they chanted.
Many protestors waved Bahraini, Iraqi and Palestinian flags and shouted: "No US bases in Muslim countries."
Some reports put the number of protesters at 3,000. Bahrain is the smallest of the Gulf states with a population of about 650,000, of whom some 250,000 are not Bahraini nationals.
'Saudi example'
"It is a crime to set the USA flag on fire - but it is not a crime for the USA to set the whole world on fire," a placard read.
Bahraini officials have urged people not to burn the American flag during protests, saying it said this harmed the country's relations with the United States.
Many protestors called on their government to follow Saudi Arabia's stand in refusing - so far - to allow US forces on its territory to be used in any war against Iraq.
In recent months Bahrainis have staged a series of angry protests against Israel and what they view as US support for Israeli Prime Minister Ariel Sharon.
Correspondents say Friday's march - organised by the National Committee for the Support of the Iraqi People - attracted fewer people than expected and was calmer than recent protests.