His comments, in a two-hour speech to 15,000 youth activists in the town of Sirte, were among the most critical expressed by Islam, who has emerged as his father's most trusted representative although he holds no government position.

Speaking to loud cheers, Islam criticised an array of alleged ills in Libyan public life, from the greed of "fat cats" in state institutions to the poor state of the health and education sectors, and called for a range of reforms.

"Our real situation, speaking frankly, is that we have no free press," he said, referring to the country's media, all of which are state owned.

"The democratic system we dream of does not exist. Everyone can say that ... Libya has no constitutional institutions. The situation is not clear and is not organised," he said.

"The new plan is to evaluate this (past) period and to start from tomorrow with a new determination and a new strategy."

Libya's political system, established in 1977, is based on the political philosophy contained in Muammar Gaddafi's Green Book, which combines socialist and Islamic theories.

The Green Book opposes both communism and Western liberal democracy and brands the setting up of political parties as "treason" and electing a parliament "charlatanism".

Last year Muammar Gaddafi, who came to power in a bloodless military coup in 1969, urged Libyans to let "freedoms blossom" but made no mention of political parties.

Both father and son have called for a revival of the private sector and condemned the Soviet-style command economy, long handicapped by stifling bureaucracy and an archaic banking system, for its failure to generate productive jobs.

Islam, in his early 30s, runs a charity group that has played a prominent role in pushing for economic modernisation and improvements in human rights.

He also played an influential role in repairing relations between Libya and the West following decades of estrangement over Western allegations of Libyan support for terrorism.

Islam on Sunday cited the Lebanese guerrilla group Hizbollah as a role model for its determination.

"All the people in Hizbollah are youths. They defeated Israel. Hizbollah achieved a victory because there is seriousness, and this is the example," he said.