Obama speaks of 'heartbreak' for family of female Isis hostage (26)
Barack Obama has said America is doing everything in its power to rescue a 26-year-old woman held by the Islamic State (IS) group.
The US president's comments came a wide-ranging interview also covering politics and a measles outbreak, a day after a Japanese journalist held by the militants was purportedly beheaded.
Mr Obama told NBC he had watched videos of hostages being beheaded.
"Every morning I get a presidential daily briefing and it gives me a pretty clear sense of the terrible stuff that's happening. And it's part of the reason why we have to be so vigilant and so aggressive in going after a vicious organisation like Isil," he said, using an acronym for IS.
Three Americans - aid worker Peter Kassig and journalists James Foley and Steven Sotloff - were beheaded last year by the terrorists. A fourth American being held is a woman captured last year in Syria while working for aid groups. She is not being identified because of fears for her safety.
"Obviously this is something that is heartbreaking for the family and we want to make sure we do anything we can to make sure that any American citizen is rescued from this situation," Mr Obama said.
On the measles outbreak, traced back to California's Disneyland theme park, that has spread to more than 100 people, the president said unvaccinated children were putting infants and others at risk. "You should get your kids vaccinated," Mr Obama said.
Some parents continue to believe debunked research linking vaccines to autism.
Obama spoke to the broadcaster before hosting a Super Bowl party at the White House for friends.
The president ducked picking between possible 2016 Democratic presidential contenders Joe Biden and Hillary Clinton. "Love 'em both," he said, smiling.
Meanwhile the wife of beheaded hostage Kenji Goto, 47, said she was devastated but proud of her husband.
In a statement issued through British-based journalist group Rory Peck Trust, Rinko Jogo requested privacy for her family as they dealt with their loss, and thanked those who had supported them.
"I remain extremely proud of my husband, who reported the plight of people in conflict areas like Iraq, Somalia and Syria," she said.
"It was his passion to highlight the effects on ordinary people, especially through the eyes of children, and to inform the rest of us of the tragedies of war."