Thousands have taken to the streets in several Sudanese towns to protest economic hardship, especially higher bread prices, with a mob in the northern city of Atbara torching the ruling party's offices, activists said Thursday.

Photos and video clips posted by the activists on social media purported to show protests in several cities in Sudan, with demonstrators chanting anti-government slogans. A video clip obtained by The Associated Press late Wednesday showed the headquarters of President Omar Bashir's National Congress Party in Atbara engulfed in flames. Vehicles parked outside were also torched.

Authorities responded by declaring a state of emergency in the city and a nighttime curfew.

Protests broke out in the Red Sea city of Port Sudan, Barbar in the north and Nohoud in the western Kordofan region. There were no reports of clashes with security forces.

After weeks of shortages, authorities hiked the price of bread by three folds to about six U.S. cents, a move that is largely responsible for the latest wave of protests. The price of a range of basic items has significantly increased over the past year, pushing inflation rates up to at least 60 percent.

This week's protests coincided with the return to Sudan of opposition leader Sadeq al-Mahdi, the country's last freely elected leader, whose government was overthrown in a 1989 military coup led by Bashir. Al-Mahdi was living in self-imposed exile outside Sudan for nearly a year. Thousands of his supporters welcomed him home on Wednesday.

Addressing supporters, al-Mahdi proposed the formation of a national unity government to tackle the country's chronic economic problems and the internal displacement of Sudanese as a result of violence.

The protests also follow the start of a campaign by lawmakers loyal to Bashir to rally support to amend the constitution to allow the Sudanese leader, in power for nearly three decades, to run for re-election in 2020.

The Sudanese leader was indicted in 2010 by the International Criminal Court for genocide during the conflict in Sudan's western Darfur region which began in 2003 and is blamed for at least 200,000 deaths.

Sudan's economy has struggled for most of the 29 years Bashir has been in power. The situation has rapidly deteriorated since the secession of the south of the country in 2011, which deprived Khartoum of the oilfields there.

In the hope of securing aid and investments, Bashir has in recent years moved closer to oil-rich Gulf Arab nations, especially Saudi Arabia. He has deployed Sudanese troops in Yemen to fight alongside a Saudi-led coalition backing the government there against Iran-aligned rebels.