Sudan's all-powerful National Intelligence and Security Service (NISS) arrested on Friday the deputy chief of the opposition Sudanese Congress Party, Khaled Omar, from his home in Khartoum.
Since then threee other members of Omar's party were also arrested, a senior member of their party, Bakri Youssef told AFP.
Three activists from the Baath Party were also arrested over the past two days, party spokesman Mohamed Diaddin said.
The opposition Communist Party also announced on its Facebook page the arrest of a senior member, Mohideen Al-Jallad.
And on Sunday, small groups of protesters burnt tyres and tried to stage demonstrations in two districts of Khartoum but they were swiftly dispersed by riot policemen, an AFP correspondent reported.
A demonstration was also held in Medani, south of Khartoum where protesters chanted anti-government slogans, witnesses said.
Overnight, security agents also seized print runs of three newspapers -- Al-Tayar, Al-Jadida and Al-Watan -- after they covered the fuel price hike in reports seen as criticial of the government.
Fuel price rises have been a sensitive issue in Sudan, where the economy has been badly hit since 2011 when South Sudan gained independence and took nearly three quarters of the formerly united country's oil reserves with it.
In September 2013, the government slashed fuel subsidies, sparking street protests as retail prices soared by more than 60 percent.
In an ensuing crackdown by security forces, dozens of protesters were killed.
Security agents often detain opposition politicians and activists for criticising government policies or President Omar al-Bashir's rule.
At least 17 members of the Sudanese Congress party were detained in August 2015 for criticising Bashir, while four members of Reform Now Party were held for similar reasons a month later.
Bashir, who came to power in an Islamist-backed coup in 1989, is wanted by the International Criminal Court on war crimes charges related to the conflict in Darfur.
Sudan's leading opposition the Umma Party vowed to oppose the fuel price hike.
"We will fight against this policy by all means. This policy is an evidence that this brutal regime must go immediately," it said in a statement.
The Sudanese Congress Party has also pledged to press a campaign against Bashir's government "until the regime has been overthrown".