The street protests, initiated by the February 20 Movement for Change which has attracted 19,000 Facebook fans after revolts in Egypt and Tunisia, will also urge the king to dismiss the coalition government and dissolve parliament.

The revolutions, especially in neighbor Tunisia, have brought the issue of constitutional reform back onto the agenda after a crackdown that followed suicide bombings in 2003 and the rapid rise of a political party led by a former security official close to the king.

On the eve of the protest, a Moroccan youth movement said it was pulling out because of disagreements with Islamists and leftists.

Morocco is officially a constitutional monarchy with an elected parliament. But the constitution empowers the king to dissolve the legislature, impose a state of emergency and have a key say in government appointments including the prime minister.

Never since his enthronement in 1999 has King Mohammed's role come under so much scrutiny. The turnout for the protests and the slogans that will be chanted will be closely watched to gauge the popularity of a monarch who shuns domestic media and press conferences.