Nicaragua's ruling elite tightened its grip on power this week after the country's National Assembly voted to bar opposition parties from future elections, a move US Secretary of State Marco Rubio has denounced as the final collapse of the country's democratic pretences.

The reform, passed unanimously in a special outdoor legislative session on Tuesday, will formally exclude from office any opposition figures deemed to have taken part in planning or carrying out a coup. It also extends the presidential term from six to seven years, along with the terms of other elected officials and the heads of the army and police.

Tuesday's vote was only the first of two required approvals: Nicaraguan law requires constitutional amendments to clear two separate legislative sessions before taking effect, and co-president Rosario Murillo has said the second vote will begin on January 18.

Rubio said the vote confirmed that Nicaragua's elections could no longer be considered free or fair, describing the National Assembly as "captive" to President Daniel Ortega and his wife, Murillo. In a statement, he said the pair had used the reform to "entrench their illegitimate dynasty" and indefinitely deny Nicaraguans the chance to vote them out.