Venezuela's national assembly has approved a controversial constitutional amendment that allows the president, or any other elected official, to stand for re-election indefinitely.

The measure, which must be put to a referendum within 30 days, is the second attempt by Hugo Chavez, the country's president, at seeking unlimited re-election.

Chavez amended the constitution in 1998, one year after being elected, to allow for a second six-year presidential term.

In 2007, however, attempts to remove term limits on his office were rejected in a referendum.

Chavez has said he plans to run for a third term if legally allowed to in 2012.

The amendment was passed on Wednesday after eight hours of debate by a show of hands in the 167-seat assembly, with only six votes against.

Allies of Chavez holds a strong majority in the legislature.

The constitutional amendment will now be presented to the National Election Board, which will convene a referendum, expected around February 15.

Hundreds of students, meanwhile, held protests against the approved legislation outside several universities in Caracas, the Venezuelan capital.

Police used water cannons and tear gas to disperse at least one group of demonstrators blocking a highway.