Sudanese Islamist opposition leader Hassan al-Turabi has been arrested by security forces at his home, his party has said.
His secretary said that armed officers had arrived in several vehicles at the house in the capital, Khartoum.
The security forces also arrested a member of Mr Turabi's staff after he clashed with them, Awad Babiker said.
On Sunday, Mr Turabi, 78, warned of a "popular uprising" if the government did not reverse new austerity measures.
The BBC's James Copnall in Khartoum says there is a growing nervousness in Sudan and other Arab countries following the overthrow of President Zine al-Abidine Ben Ali in Tunisia last week.
On Monday, Mr Turabi warned that an uprising as seen in Tunisia was "likely" amid public anger over poverty, a lack of political reform, and fears over the likely secession of Southern Sudan.
"This country has known popular uprisings before," he told the AFP news agency, referring to revolts in Sudan in 1964 and 1985. "What happened in Tunisia is a reminder. This is likely to happen in Sudan."
"If it doesn't, then there will be a lot of bloodshed. The whole country is armed. In the towns it will be a popular uprising, but in Darfur, and in Kordofan as well, they have weapons."
Mr Turabi has been accused of links to rebels in Darfur - something that he has always denied.
"Sudan is not a small country like Tunisia, but it is exposed to a risk of chaos worse than Somalia," he said.
Southern Sudan is on the point of splitting away from the north, having voted in a referendum last week.
The south has most of the country's oil reserves, so the blow to the north's economy will be sizeable, our correspondent says.
On Sunday, opposition parties, including Mr Turabi's Popular Congress Party (PCP), called a joint news conference to congratulate Tunisians and demand an "end to the totalitarian regime" in Khartoum.
They also threatened to take to the streets if the president did not sack the finance minister and reverse a recent decision to raise prices on a range of basic goods.
Sudan is suffering an economic crisis, with a current account deficit and currency devaluation driving up inflation.
"All the opposition parties have been talking to the government again and again to try and get them to decentralise, to liberalise, to democratise and promote freedom of expression. But they don't allow it," Mr Turabi said.
Mr Turabi, a close ally of President Omar al-Bashir until 1999, has been detained several times since he set up the PCP.
He spent six weeks in detention in 2010 after he repeated an allegation that April's presidential election had been rigged.