Riot police fired tear gas and civilians armed with machetes and swords attacked protesters during five days of demonstrations sweeping Khartoum, demanding the exit of Sudan's autocratic ruler, a Sudanese opposition leader has said, Belfast Telegraph reported.

Saata Ahmed al-Haj, head of the opposition Sudanese Commission for Defence of Freedoms and Rights, said that hundreds of protesters have been detained over the past five days. He said they were later released but were badly mistreated.

Al-Haj said security forces shaved off the protesters' hair, stripped them naked, flogged them and then left them outside in the scorching sun for hours.

A government austerity plan slashing subsidies and doubling the price of fuel and food set off the protests. President Omar al-Bashir has said the measures are necessary to pay for his country's conflict with South Sudan and to replace Sudan's oil revenues. He said Sudan no longer exports oil.

On Thursday, al-Bashir issued new decrees to cut expenditures as "part of the austerity plan," according to Sudan's official news agency Suna.

The demonstrations started on Saturday night at the University of Khartoum. Students protesting against transportation fare hikes took to the streets outside the downtown campus, where security forces fired tear gas and rounded up dozens of them. Since then, Khartoum has been the scene of daily protests, spilling out to different of the capital.

Echoing calls heard in Arab Spring uprisings in Tunisia, Egypt, Libya and Syria, protesters chanted: "The people demand to bring down the regime."

Al-Bashir, 68, has ruled Sudan since 1989, when he carried out a bloodless military coup. Sudan was then in midst of two decades of civil war with the south, which declared independence last year and became the nation of South Sudan.