"The armed forces will not allow constitutional order to be broken or any action against democracy and the laws of the republic," Defense Minister Luis Lara, accompanied by military commanders, told journalists.
"We urge Ecuadoreans toward national unity," he said, adding that drug traffickers and organized crime were behind the violence that had broken out at the protests. At least 55 protesters and 61 members of the security forces have been injured in the violence.
Lasso, who took office 13 months ago, has repeatedly blamed drug gangs for rising violence, including prison riots which have killed hundreds.
"This uprising is because of poverty and inequality," said Leonidas Iza, leader of CONAIE, an indigenous group. "No one is against anyone. We are against corruption, the injustice which has caused a deterioration in the majority of Ecuadorean society."
Fuel subsidies cost the government some $2.8 billion a year.
The protests have prevented some 102,000 barrels of crude from being produced, the energy ministry said in a statement. State-run oil company Petroecuador declared force majeure on Saturday.
