Muslim protests have been taking place in France and other countries against a French bill which would ban headscarves from state schools.
Some two dozen separate protests were planned worldwide
Up to 5,000 protesters, mainly Muslim women in scarves, rallied in Paris.
President Jacques Chirac announced a ban on overtly religious symbols in schools last month after an official report into state secularism.
Many of France's five million Muslims see it as an attack on their religious and human rights.
Apart from the Islamic headscarf, the ban - scheduled to be enacted before the next academic year in France - would also affect the Jewish skullcap, big crucifixes and Sikh turbans.
The government proposed the new law as a measure to safeguard France's secular tradition.
The afternoon demonstrations in Paris and other French cities were organised by a small group, the Party of French Muslims (PMF), which is regarded by many in France as a radical Islamist organisation, the BBC's Alan Little reports from Paris.
Protesters in London chanted "Stop Chirac's racist war!"
One banner condemned "secular fundamentalism".
An estimated 2,400 opponents of the ban rallied in London, where there was also a small counter-demonstration.
"The Islamic hijab is enslaving women, not freeing them," Sohaila Sharifa, one of the 30 or so counter-demonstrators, told the Associated Press.
Outside the capital cities, including Brussels where about 1,000 protesters appeared, the largest demonstrations were held in the French regions. There were small rallies, too, in the Middle East.
An estimated 3,500 marched in Lille, 1,800 in Marseille, 1,500 in Mulhouse and hundreds in other French cities, police and organisers said.
Scores of Muslim women and girls demonstrated outside the French embassies in Beirut and Amman, while in the Palestinian territories about 300 women turned out in the West Bank city of Nablus.
Mr Chirac's stand reflects popular opinion in France where some 70% of the electorate have said they back a ban on religious symbols in schools.
The French Government has criticised the rallies as an attempt to stir up racial tensions.
Spokesman Jean-Francois Cope defended France's strict separation of church and state, saying it provided freedom to exercise one's faith while respecting that of other people.
"As for the demonstration, we see very clearly that some can and are being tempted to radicalise things, to twist reality," he said in an interview on Radio Classique.
Appeal for calm
Divisions have emerged within France's Muslim community over tactics.
President of the French Council of the Muslim Faith (CFCM) Dalil Boubakeur,
who warned that the law "could stigmatise a whole community", urged Muslims not to take part in demonstrations.
One of the largest groups within the CFCM, the Union of Islamic Organisations of France (UOIF), called for demonstrations to be peaceful.
"We call on the Muslims of France to demonstrate calmly, peacefully and responsibly in a citizen-like way and without provocation that risks betraying our noble cause: the defence of fundamental liberties, in particular, religious freedom," the UOIF said on its website.