The Chamber of Deputies approved the bill - which was sponsored by Kirchner's former chief of staff and had already passed the Senate - by 131 votes in favour to two against and one abstention.

Voting is compulsory for Argentines aged 18 and older - some 29 million people - but will be optional for those aged 16 and 17, some one million people.

"It is a very important initiative because it expands the frontier of rights," said Agustin Rossi, head of the governing bloc in the lower chamber.

Kirchner has actively courted the youth vote, and the latest move could help her party tighten its grip on parliament in the October 2013 elections.

Critics have said the move is aimed at winning a large enough majority to change the constitution in order to allow Kirchner to seek a third term the following year.

Supporters of the bill - sponsored by Senator Anibal Fernandez, Kirchner's former chief of staff - argue that young people are more politically aware than before and point to neighbouring Brazil, which also allows voting at 16.

Some lawmakers are also seeking to grant foreigners - seen as another pro-Kirchner group - the right to vote if they have at least two years of permanent residence in the country.

About half a million people are estimated to fall into that category.