Newt Gingrich has decided to quit the US presidential race and will announce next Tuesday that he is no longer seeking the Republican nomination, sources quoted by US media said.

The former speaker of the House of Representatives will "more than likely," endorse presumptive Republican nominee Mitt Romney as he announces either the suspension or the end of his own campaign, a source told Fox News.

NBC news said on its website that Gingrich would suspend his campaign on Tuesday 1 May, and could endorse Romney.