The United States on Tuesday accused Nicaragua's government of "repugnant" violence and repression against protesters demanding the ouster of the president.
Following a massive anti-government march in the capital Managua on Monday by tens of thousands of workers, students, pensioners and ordinary citizens, an embattled Ortega has stepped up appeals for dialogue.
The president' hastily canceled the pension reform at the weekend, but that failed to attenuate the protests.
He has also ordered the release of dozens of protesters arrested during the protests and lifted a broadcast ban on a private TV news channel.
The concessions appeared to be mollifying the country's business elite, which had abandoned a longstanding alliance with Ortega over the violence.
But the situation remained tense and uncertain, with students vowing to maintain their campaign to force Ortega from power and police showing no signs of pulling back.
The US condemned the violence, repression and the closing of media outlets, it added, calling for "broad-based dialogue and support for the people of Nicaragua, who yearn for the political freedom of expression and true democratic reforms they so richly deserve".
The US embassy has already withdrawn staff family members and non-essential personnel.
Although there have been periodic protests over the last few years related to specific issues such as a proposed shipping canal project, "the scale and scope of these protests, which have caught a number of people by surprise, reflects an anger in some groups that has been building for years", Christine Wade, of Washington College in Maryland in the US, told RFI.
Will the call by the United Nations for an investigation into the government's handling of the protests make any difference to the situation?
"I think the government is going to find that it's got little choice but to either launch an inquiry or to support an inquiry from the outside" says Wade. "This might have started as a policy protest but it has very quickly become about how the government and its affiliated bodies responded to these protests.
"Nicaraguans I've spoken to of all political affiliations are demanding answers and justice for those who were killed ... and I don't see that going away. I think it's in the best interest of the Ortega administration not to ignore this."
Managua Archbishop Leopoldo Brenes said he was willing to serve as "mediator and witness" in any talks, but warned that first the government must "avoid any act of violence".