Egypt's Interim President has signed a new bill into law restricting rallies and other public gatherings.

The move by Adli Mansour has raised fresh questions about the army-backed government's democratic credentials.

Thousands of anti-government protesters were on the streets of Cairo and other cities when the new bill was announced on state media.

The new legislation will require them to get advance permission from the police before gathering in the future, according to a draft.

"This is quite dangerous ahead of elections - in normal times also, but [particularly] ahead of elections," said Ziad Abdel Tawab of the Cairo Institute for Human Rights, adding it could disrupt public meetings including debates and rallies.

Mr Mansour's approval of the law came as a 50-member committee prepared to vote on an amended constitution that will be put to a referendum expected in coming months.

Parliamentary and presidential elections are due next year.

Rights groups had urged Mr Mansour to reject the draft presented to him by the cabinet installed after the army overthrew Hosni Mubarak's successor, Islamist President Mohammed Mursi, in July.

"The draft law seeks to criminalise all forms of peaceful assembly, including demonstrations and public meetings, and gives the state free hand to disperse peaceful gatherings by use of force," said 19 Egyptian organisations in a joint statement.

Thousands of supporters of Mr Mursi and his Muslim Brotherhood demonstrated in Cairo and in several other cities, marking 100 days since security forces crushed two pro-Mursi sit-ins in Cairo, killing hundreds.

Police fired tear gas to disperse some of the demonstrations earlier.

There was no immediate sign of any reaction to the new legislation on the streets.

The Muslim Brotherhood has faced a harsh security crackdown since Mr Mursi's removal from power. Thousands of supporters have been arrested and its senior leaders have been jailed.