Rosamund Pike ''wavered in courage'' when she portrayed Marie Colvin in the film 'A Private War'.

The 39-year-old actress plays the lead role in the Matthew Heineman drama - based on the life of celebrated war correspondent Colvin - and she revealed that it was ''scary'' playing the Sunday Times reporter because the filmmaker would want to put her in ''unstable'' scenarios.

Speaking to the Radio Times about how she portrayed the journalist, she said: ''I'm a very passionate person and not half as reserved as people imagine. I know I can put that across; I think it's just as dangerous to let it out too much.

''It's quite scary playing someone like Marie because you're getting in touch with some things that are very unstable. And Matthew's way of working is inherently unstable, because he's looking for things that are not prepared.

''It made me feel like I wavered in courage at times. You know: could I do it? Well you know you are a shape-shifter in your core, really. My business is to transform, and I will.''

The blonde beauty improvised a scene with genuine refugees from Syria and Iraq in the Homs suburb of Baba Amr when she was filming for the movie.

Pike admitted that she became affected by a scene when a man - who's two-year-old nephew had been killed by an Assad regime bullet - appeared as a father that had lost his son, and ''erupted in grief'' when he saw the true-to-life film set.

She added: ''People underestimate how real a film set can feel, I think. So, when this man saw our baby on the gurney, this grief erupted out of his body and engulfed the room.

''I didn't know where to put my feelings and they exploded in me. I thought, 'What right do I have to be here? This, for this man, is real, and I'm not real. Who am I?''