At least 50,000 people took part Monday in the biggest demonstration yet in Bangladesh over French President Emmanuel Macron's defence of the right to publish cartoons of the Prophet Mohammed, police said.

A rally which started at Bangladesh's biggest mosque was stopped from getting close to the French embassy where security has been stepped up.

Police estimated some 50,000 people took part in the protest, which demanded a boycott of French products, while organisers said there were more than 100,000.

Protesters chanted "No defamation of the Prophet Mohammed" and burned an effigy of the French leader.

Macron sparked protests across the Muslim world after the murder last month of teacher Samuel Paty -- who had shown his class a cartoon of Mohammed -- by saying France would never renounce its laws permitting blasphemous caricatures.

The third major anti-France demonstration in Bangladesh in the past week was called by Hefazat-i-Islami, one of the biggest radical Muslim political groups in the country of 160 million people.

Many people came from towns outside Dhaka to take part in the rally.

Junaid Babunagaori, the firebrand deputy chief of Hezafat, called on Prime Minister Sheikh Hasina to move the Bangladesh parliament to condemn Macron.

"I call on traders to throw away French products. I ask the UN to take stern action against France," he told the rally.