The widow of murdered aid worker David Haines has said the Islamic State militants who killed her husband are 'cowards'.

Speaking at their home in Sisak, Croatia, in her first television interview for Sky News, Dragana Haines said: "They consider themselves brave, but that's not bravery.

"It's a cowardly act to behead someone who has his hands tied behind his back, who is kneeling.

"You are a coward if you are going to behead someone who is helpless. You're not even a human being. You must be a monster to do something like that."

Mr Haines grew up in Scotland and served as an aircraft engineer in the RAF, but he found his calling in humanitarian work.

He met Dragana, his second wife, in post-war Yugoslavia.

He was working for a German reconstruction charity, and she was a translator for the Organisation for Security and Co-operation in Europe (OSCE).

They married in 2010 and settled in Croatia, where their daughter, Athea, was born.

In March 2013, he was kidnapped while working for a French aid agency in Syria.

"Every day was a challenge," Mrs Haines said.

"Waking up in the morning and thinking OK should I be hopeful? Will it be a day when they will call me, or he will call me and say 'OK I'm free, I'm coming back'?

"Or will it be a day when they will call me and say something bad has happened?"

In June, Islamic State released a video showing Mr Haines, and warning he would be next to be killed.

"I saw him in the video," Mrs Haines said through tears.

"I just saw the part when he was talking. I never found enough strength to see the rest of the video. I don't want to see it."

She tried to hide her anguish from their four-year-old daughter, but the little girl realised something was wrong.

Mrs Haines said: "I was trying to go to my room so she wouldn't see me crying, but of course she heard me.

"After a few times she realised that as soon as I start speaking in English to someone on the phone, that it was Uncle Mike (Mr Haines' brother), she would run and bring me handkerchiefs and say 'Mum don't be sad, please don't cry', because even she understood that something wrong was going on."

In September, he called to tell her that the worst had happened, and that her husband had been murdered.

"He just told me, 'Dragana, they can't hurt him any more'. That was a moment that marked me for the rest of my life."

She still doesn't know how to explain what has happened to their daughter - why her daddy won't be coming home.

She tells her that her father was a brave man, that he went to help people in need, and that it's just the two of them now.

"David gave sense to my life," she said.

"He made it something different, he changed it - and now Athea is my reason to go on. David would want me to be strong, for our daughter."