Nouakchott - Thousands of people gathered in the Mauritanian capital Nouakchott on Saturday to protest against a move by President Mohamed Ould Abdel Aziz to abolish the senate.The president, who seized power in a coup in 2008, announced on Tuesday that he would hold a constitutional referendum that would remove the senate and replace it with a "regional council".The protesters massed under the banner of a coalition of 10 opposition parties, which promised further protests if the president continued to "provoke", and chanted slogans including "Get out", "No to the gang of predators" and "No to the extension of mandates"."Our protest today it to tell Ould Abdel Aziz that the constitution is a red line," said Saleh Ould Henenna, president of the opposition's Forum for Unity and Democracy (FNDU), addressing the rally in the centre of Nouakchott."The opposition will not accept entering into a dialogue when Ould Abdel Aziz has already defined the themes, but only to a process of consultation that would include guarantees and subjects that have been adopted by consensus," he added.Former general Abdel Aziz said on Tuesday there would be a political dialogue ahead of the referendum, and that he would give the opposition "three to four weeks" to decide if they wanted to take part. He did not give a date for the vote.In his speech he did not make reference to claims by the opposition that he was attempting to seek a third term in office, but said it was "quite normal" for the government to re-examine the constitution.However, several government members said they were in favour of a change to the constitution to allow Abdel Aziz to run for a third term.Abdel Aziz came to power in a coup in 2008. He was then elected president in 2009 and again in June 2014 for a second five year term.