More than 1,000 Islamists rallied in Cairo on Friday and called for the implementation of sharia Islamic law, highlighting divisions in society as rival factions jostle to shape the new Egypt.

Liberals have locked horns over the role of Islam with Islamists who dominate a 100-strong assembly that is drawing up a new constitution, which must be approved in a referendum before a new parliamentary election can be held.

"Islamiya, Islamiya," the protesters chanted in Cairo's Tahrir Square, the centre of the uprising that toppled Hosni Mubarak who spent 30 years keeping a tight lid on Islamists.

The turnout at Friday's demonstration was smaller than had been expected after some of the main groups that espouse the ultraconservative Salafi school of Islamic thinking backed out. Some groups said they would demonstrate next Friday.

The Muslim Brotherhood, which propelled President Mohamed Mursi to power earlier this year and which takes a less conservative approach, was also not involved in the protest.

Unlike many of the rallies since the fall of Mubarak that have packed the square, Friday's numbers were modest and traffic flowed with relative ease even as the demonstration went on.

"No to liberalism, no to secularism, I don't want anything other than sharia," the protesters also chanted, some waving black flags emblazoned with Islamic slogans.

Drafts of the constitution drawn up by the assembly so far indicate it will have more Islamic references than the previous constitution, worrying more liberal-minded Egyptians and Christians, who make up about a tenth of the nation of 83 million. They fear the imposition of social restrictions.

A key article stating that "the principles of sharia" are the main source of legislation has until now remained unchanged from the old constitution but a new article seeks to spell out what those principles are in Islamic terms.

However, that is not enough for many Salafis who want an unequivocal call to implement sharia rather than wording that they say liberals will use to water down the meaning.

"I want Islamic sharia to be the only source of legislation, not the 'main source'," said Hany Mohamed Ahmed, a 38-year-old Finance Ministry accountant, who was among those demonstrating.