Egypt's fast-growing 'Rebel' campaign, which is collecting signatures for a vote of no confidence in President Morsi, has launched an official website.

The campaign, which officially opened on 1 May, had around 3 million signatures by last week, according to organisers.

A press conference will be held within the next couple of days to give an update on the number of signatures collected.

The initiative has been backed by a large number of political parties and high-profile political figures.

Allies of the president have been quick to condemn the campaign, with some calling it illegal and unconstitutional.

'Rebel' campaigners have reportedly been attacked – allegedly by Islamist supporters of the president – and briefly detained while collecting signatures.

When asked about the campaign during his current visit to Ethiopia's capital Addis Ababa, President Morsi said those involved should not forget the key principles of democracy.

"Some people say that I barely got 52 percent of the votes in [last year's] presidential election [runoff against Ahmed Shafiq], but legally and constitutionally I am the legitimate president," Morsi said.

'Rebel' hopes to collect 15 million signatures in support of a vote of no confidence in President Morsi, outnumbering the 13.2 million votes he won in Egypt's first-ever free presidential poll in June 2012.

The campaign hopes to conclude with a million-strong rally outside the presidential palace in Cairo to demand immediate presidential elections. The petition will be submitted to the public prosecutor.

The website – www.tamarod.com – is geared towards collecting signatures online and is available in Arabic, English, French and German.