A 2008 speech in which Rick Santorum declares "Satan is targeting" the United States has resurfaced on the campaign trail, even as the Republican presidential hopeful faces controversy over recent comments questioning President Barack Obama's "theology."

Gunmen attacked worship services at a university campus and a church in northern Nigeria, killing at least 21 people in co-ordinated assaults that saw Christians gunned down as they tried to flee, witnesses and officials said.