Image copyright Getty Images Image caption Amira Hamzeh (2nd left) is the Al Jazeera newswoman arrested by security officials in Sudan
Six people have been killed and 100 injured during clashes between anti-government protesters and security forces in Sudan, according to activists.
At least two opposition leaders and two journalists were among those arrested, according to the UK-based Sudanese Professionals Association.
Last week protesters defied a 12-hour curfew to march on the ministries in the capital, Khartoum.
Thousands of people took to the streets last month over President Omar al-Bashir’s plans to amend the constitution.
The reforms include removing presidential term limits that limit him to two terms in office.
Demonstrators reject the decision and some media reported that several hundred people had taken part in Friday’s protests.
“Some people were shot dead on the street, others have died of live bullets,” said Naif Abdel-Latif, head of the National Umma Party.
He called for the resignation of the government.
Amnesty International said Sudanese police were arresting political leaders, journalists and activists.
“Amnesty International is alarmed at the use of excessive force, and the harassment and arrest of Sudanese human rights defenders,” the Amnesty said in a statement.
It said that journalists and journalists have also reported being threatened and detained for reporting on the demonstrations.
In June, the government approved the referendum law, allowing people aged between 18 and 30 to vote on whether to abolish the capital’s term limits and for the president to serve for two terms.
The move followed a referendum last year which saw 70% of Sudanese voted to abolish the republic and amend the constitution.
The last election took place in 2010, when Mr Bashir was re-elected with 95% of the vote.
Before being elected in April, Mr Bashir, who is an internationally wanted war criminal, secured a new five-year term.
He was wanted by the International Criminal Court for alleged war crimes and genocide in the Darfur region.
Sudanese authorities said last month that 3,000 demonstrators had been arrested and 5,000 people had been arrested since last month.
“There are huge forces using live bullets in downtown Khartoum,” Adam Omer, the chief of staff for the deputy interior minister told Al Jazeera, describing the crackdown.
The government has refused to offer any details of the alleged arrests.