Vice President Joe Biden yesterday made an impromptu trip to support a group of nuns who are running a campaign to increase voter turnout.

After flying to Des Moignes, Iowa, in Air Force Two, Biden gave an impassioned address to a crowd who had gathered to support 'Nuns on a Bus'.

A group of 11 sisters are planning to travel around ten states in order to encourage American citizens to participate in the electoral process. The tour is non-partisan, though the nuns are recognised as a liberal group.

Biden, himself a Catholic and possible Democratic candidate for the 2016 presidential elections, used his address to denounce the increasing gap between rich and poor in America, stating: "It's a question of basic fairness."

"Basic, simple, decent fairness. This isn't a popularist rant, this is about how we rebuild America."

His visit followed Hilary Clinton's own trip to Iowa just three days earlier, which has led to increased speculation about his potential bid for presidency, but Biden insisted he has not yet "made a decision to run or not run for real".

"There's plenty of time to make that decision. And that's the least of my worries and concerns right now," he told the Guardian.

Sister Simone Campbell, who leads the Nuns on a Bus campaign, said on Wednesday that voting is important because it's like "having job interviews for a bunch of politicians."

The nuns hope to "create a more perfect union" by encouraging voter engagement, she added.

"Democracy works best when everyone has a seat at the table," Biden explained.

"I know no group of people who bring more passion to what they do," he said of the group of sisters.