Salma El Wardany, an Egyptian, was held on Thursday a day after AFP correspondent Simon
Martelli, a Briton, was released after more than 12 hours in custody without charge.
Both were detained by intelligence officers at the University of Khartoum, where riot police have violently dispersed a string of protests since last Saturday.
Daily demonstrations against high food prices and calling for regime change have spread to other parts of the city.
Wardany said she and a female Sudanese journalist were parking at midday outside the downtown university campus when “six big men” approached, shouting and pounding on their car.
“What are you doing? Are you taking photos?” she said they asked, before seizing their laptops and taking them to the outskirts of the city for interrogation.
The men did not identify themselves, she said, adding that a witness saw what happened and reported it on the Twitter social networking site, which led to a “huge campaign” for their release.
“They were calling the foreign ministry in Egypt, the embassy here, Bloomberg,” Wardany said.
She added that she was freed without charge and had no access to a telephone or lawyer while detained.
Wardany said the security agents barred her from working as a journalist unless the country’s press council decides otherwise.
Her Sudanese colleague was also released.
The security forces have pursued a zero tolerance policy towards dissent in recent days.
They seem particularly sensitive to demonstrations outside the University of Khartoum, where protests in 1964 ultimately led to a mass uprising that toppled the military dictatorship then in power, in what became known as the October Revolution.
Inflation has risen month after month, hitting 30.4% in May, and prices are expected to rise further after Finance Minister Ali Mahmud al-Rasul on Wednesday announced austerity measures including the scrapping of fuel subsidies.
Bankrupt Sudan has lost billions of dollars in oil receipts since South Sudan gained independence last July, leaving Sudan plagued by inflation, a severe shortage of dollars needed to pay for imports, and a currency plunging in value.
Press freedom advocates have described an intensifying clampdown on critical voices in recent weeks, including the seizure of newspapers after printing- AFP