Nicaragua's president on Saturday ruled out bringing forward elections scheduled for 2021 by two years to quell unrest following months of clashes which have left 310 people dead.

Speaking to supporters and state employees, President Daniel Ortega pointed to the country's constitution, which stipulates that elections are held every five years.

"Here, the rules are put in place by the Constitution of the Republic, through the people," Ortega said. "The rules cannot be changed from one day to the next because of a group of putschists," without identifying who he thinks is behind any alleged coup attempts.

The crisis gripping the central American nation began on April 18 with protests against social security reforms, to which authorities responded with an aggressive crackdown, various NGOs and international observers have said.

There have also been allegations of illegal detentions and of police abuse made by the Inter-American Commission on Human Rights (CIDH) and the Office of the United Nations High Commissioner for Human Rights, who accuse the government of grave violations.

Among these violations, the groups cite "assassinations, extrajudicial executions, mistreatment, torture and arbitrary detentions," the CIDH said, allegations the government rejects.

Ortega has been in power since 2007, winning re-election in 2011.

In 2014, the country's national assembly approved measures which abolished presidential term limits, allowing a president to run for an unlimited number of five-year terms.

The crisis is the bloodiest the country has known since the 1980s, when Ortega was also in power during his first term in office.