Security forces have arrested scores of protesters, opposition members, and journalists, beat people in detention, and used rubber bullets and live ammunition to break up protests that began on June 16, Human Rights Watch said in a report released on Tuesday.
Sudan should end the crackdown on peaceful protesters, release people who have been detained, and allow journalists to report freely on the events, the report added.
"Sudan is using these protests as an excuse to use violence and intimidation to silence dissenters," said Daniel Bekele, Africa director at Human Rights Watch.
"Authorities should call off their security forces and vigilantes, end the violence immediately, and respect the right of the people to protest peacefully."
"Arresting all suspected opponents to stifle dissent is abusive and illegal," Bekele said.
"Authorities need to charge or release these detainees immediately, allow people to voice their opinions peacefully, and let the media work freely."
The protests began on June 16 at Khartoum University in response to government austerity measures and price increases, and they had spread to dozens of other locations in Khartoum, and other towns across Sudan, with protesters calling for the end of the current government.
Meanwhile, the US have condemned the crackdown on Sudan protests,"Sudan's economic crisis cannot be solved by arresting and mistreating protesters," said State Department spokeswoman Victoria Nuland.
"There have been reports of protestors being beaten, imprisoned and severely mistreated while in government custody.
We call for the immediate release of those detained for peaceful protest," she added in a statement.
The National Security and Intelligence Services (NISS) on Tuesday deported Salma El Wardany, an Egyptian female correspondent of Bloomberg News in Khartoum, and briefly detained prominent Sudanese blogger Maha El Sanousi.
"They ordered me to leave," Salma El Wardany, an Egyptian, told AFP by telephone as she awaited a flight from the Khartoum airport.
Sudan has lost billions of dollars in oil receipts since South Sudan gained independence last July, taking with it about 75 per cent of Sudanese crude production. The north has been left struggling for revenue, plagued by inflation, and with a severe shortage of dollars to pay for imports.
The landlocked South depended on the north's pipeline and port to export its crude, but Khartoum and Juba could not agree on how much South Sudan should pay to use the infrastructure.
Sudan's already depleted oil revenues shrank by a further 20 per cent after its main Heglig oil field was damaged and shut down in fighting with invading South Sudanese troops in April, international economists have estimated.
Even before the easing of fuel subsidies, the cost of basic consumer goods had doubled over the past year.
Bashir, an army officer who seized power in 1989, called the protests small and not comparable to the "Arab Spring" uprisings against regional strongmen over the past year.
He blamed anti-government protests on the work of "a few agitators" in a speech late Sunday.
But a demonstrator told AFP the current unrest is unprecedented. "Right now, this is first time since 1989 we have these protests in most cities," he said, asking not to be identified by name.
There have been calls on social networks for a mass nationwide protest on June 29.