Obama slams Republicans for pushing ideas from "last century"

President Barack Obama set out to boost his re-election bid on Saturday with a scathing critique of the Republicans' convention.

Speaking to a crowd of 10,000 in the battleground state of Iowa, Obama said his Republican rival Mitt Romney and his party had not offered any fresh ideas during their national convention in Tampa, Florida last week.

"What they offered over those three days was more often than not an agenda that was better-suited for the last century…We might as well have watched it on a black-and-white TV,” said Obama.

Obama criticized Romney for failing to discuss foreign policy such as the war in Afghanistan or plans to lift the economy.

"There was a lot of talk about hard truths and bold choices ... but no one ever actually bothered to tell you what they were," Obama said.

Obama’s comments come ahead of the Democratic convention in Charlotte, North Carolina, which kicks off on Tuesday.

The incumbent is expected to urge supporters to cast their ballots as early as possible.

Although the November 6 election is months away, voters can begin casting their ballots in the next coming weeks.

Polls open in Iowa on September 27, while Virginia, another crucial battleground state, begins voting on September 22.

Early voting formed a large part of Obama's success in 2008. Nearly a quarter of the 133 million people who voted that year had cast their ballots before election day.

According to previous polls, Democratic voters across several swing states are more likely to vote early in comparison to Republicans.