Sudanese authorities have released a senior opposition leader who had been detained since December in connection with demonstrations against President Omar al-Bashir's rule, his party said on Tuesday.

Sudan's main opposition party on Saturday dismissed President Omar al-Bashir's declaration of a state of emergency, saying protesters would keep up their campaign until his three-decade rule was ended.

On Friday, Bashir imposed a nationwide state of emergency and dissolved the federal and provincial governments in a bid to quell two months of almost daily demonstrations that have rocked his iron-fisted regime.

Tens of thousands face starvation in South Sudan, aid agencies warned Friday, as fighting continues despite a peace deal signed six months ago meant to end civil war.

Nearly seven million people or two-thirds of the country face extreme hunger, the government and UN agencies said.

Hundreds of Sudanese rallied on Thursday, including at a camp for people displaced by war, witnesses said, after campaigners called for anti-government demonstrators to show support for millions affected by conflicts.

Two protesters were killed during anti-government demonstrations that rocked Sudan's capital in the past day, police spokesman General Hashim Abdelrahim told AFP early Friday.

Sudanese police fired tear gas at hundreds of protesters trying to march on the presidential palace in Khartoum as anti-government demonstrators raised pressure on President Omar al-Bashir to resign with calls for nationwide rallies on Thursday.

Sudanese police fired tear gas at crowds of demonstrators in the capital's twin city  Omdurman Tuesday protesting against the fatal wounding of a demonstrator last week, witnesses said.

The anti-government protests rocking Sudan for the past month are reminiscent of the Arab Spring uprisings of nearly a decade ago. Demonstrators, many in their 20s and 30s, are trying to remove an authoritarian leader and win freedoms and human rights.

Activists challenging President Omar al-Bashir's autocratic rule say they have learned from their Arab Spring counterparts and introduced tactics of their own. That and their persistence appear to pose a real threat to the 29-year rule of the general-turned-president.

Sudanese police fired tear gas on Sunday at protesters ahead of a planned march on parliament in Omdurman, the twin city of Khartoum, witnesses said.

Sudanese protester Aseel Abdo said she had to leave her family home after being threatened with arrest for joining demonstrations against President Omar al-Bashir that have rocked the country.