But Ortega, the man who has dominated the Central American country's politics for the past four decades, only appeared to dig in deeper, defying seven weeks of anti-government protests that have left more than 100 people dead and are turning increasingly violent.
In the city of Masaya, once a bastion of support for Ortega's leftist Sandinista movement, residents put up barricades to keep out riot police and protect themselves from what they said were police and paramilitary snipers positioned around a central neighborhood.
Five people were killed in the city, including a 15-year-old boy, according to the Nicaraguan Association for the Protection of Human Rights (ANPDH).
"The blood spilled in Masaya has made it a day of mourning and pain for those citizens who simply wanted to exercise their right to protest," the head of the rights group, Alvaro Leiva, told AFP.
"We are facing a situation of profound crisis in terms of human rights violations."
A police intelligence officer was also among the victims, he said.
Separately, US Ambassador Laura Dogu said an American citizen had been killed overnight in the capital, Managua.
The ANPDH identified him as Sixto Henry Viera, 48, and said he was reportedly killed by a pro-government mob.
The police meanwhile reported looting, fires and riots in at least six cities, including Managua and Masaya, blaming "right-wing groups" -- though in at least some of the cities, residents said the security forces themselves were responsible for the destruction.
Urban battleground
Masaya, a city of just over 100,000 people, resonated with gun and mortar fire as residents vowed to fight back the security forces they blame for killing innocent protesters, as well as government supporters they say have been looting and pillaging.
Holed up in a police station and other strategic spots, police returned fire with tear gas and, allegedly, live ammunition.
Jonhatan Jose, 47, said his neighbor was shot and killed.
"They are attacking the Nicaraguan people. They put a bullet in my neighbor's chest this morning," he told AFP.
"It was a sniper... You can tell by the size of the hole -- big... He must have been about 23 years old, with a son who was three or four."
One focal point in the unrest was a burned-out artisans' market.
The government said residents had torched it, and that security forces were sent into the city at the request of small business owners who lost everything.
Residents called that a lie; they said riot police burned the building themselves in an attempt to justify the crackdown, which led to 31 arrests.
The street battles shut down any semblance of normal life in the city.
As hundreds of youths gathered at the barricades brandishing homemade mortars, machetes, rocks and slingshots, other residents sheltered in their homes in terror.
At her family-owned grocery store, 49-year-old Vanesa -- who declined to give her last name, fearing for her safety -- choked up as she described hiding out with her three children and grandson.
"I'm hopeless, heartbroken, I don't have words to describe it," she said. "The situation is horrible. Horrible, horrible, horrible."
Long fight
Protesters have a single demand, said Azhalea Solis, an opposition leader: "Get rid of Ortega's government immediately."
But the 72-year-old president looks ready for a long fight.
On Wednesday, a Mother's Day march in support of mothers who have lost children in the violence was met with gunfire that left at least 16 people dead.
Former Ortega ally Henry Ruiz -- who was a commander in the Sandinista guerrilla army when it overthrew the dictator Anastasio Somoza in 1979, bringing Ortega to power -- warned the country to brace for more.
"There is abundant evidence that Ortega will dig in militarily to fight back and strengthen his hand for negotiations," he said in an opinion column.
Ortega, who was voted out of office in 1990 and returned to power in 2007, is now serving a third term that is due to end in 2022.
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