Speculation that Condoleezza Rice is being vetted by Mitt Romney as a possible running mate has been ratcheted up after Rice got an enthusiastic thumbs-up from Sarah Palin.

Palin, the former Alaska governor and John McCain's 2008 vice-presidential pick, gave Rice her backing in a move that is expected to fuel the rumour mill and continue debate over whether the former secretary of state would return to political life.

"She [Rice] has much more experience than our sitting president does today," Palin told Fox News host Greta Van Sustren.

Palin added that she believed Rice would make a "wonderful" vice-president if the Republicans were to reclaim the White House in November's election.

Rice's name first emerged in the stakes to be Romney's running mate when the conservative Drudge Report last week claimed that the Republican challenger was considering her as a possible pick.