This was meant to be a new era for Sudan. Last year the United States ended two decades of sanctions that President Omar Hassan al-Bashir had long blamed for his country’s poverty and isolation, a move that promised new investment, perhaps even an economic rebirth.

But when Mr. Bashir then ended fuel and wheat subsidies, at the suggestion of international lending partners, protests broke out.

And over the past week, festering public anger compounded by nearly 30 years of frustration over corruption and economic mismanagement has grown into demonstrations so big and widespread that some say they could topple Mr. Bashir’s military government, or at least seriously challenge its legitimacy.

Sudan, a predominantly Arab country on the edge of sub-Saharan Africa, entered its sixth day of protests on Monday, with more planned later this week, including a mass procession to the presidential palace, an elaborate Chinese-built complex opened only three years ago.