Peter Theo Curtis, released from two years of captivity in Syria, has said he is "overwhelmed with emotion" in a brief statement to reporters outside his mother's home in Massachusetts.

He said he is grateful for all the "brave, determined, big-hearted people" who worked for his release.

The 45-year-old was released on Sunday.

Afterwards, his mother said in a statement that she was grateful for the help provided by the government of Qatar, as well as others.

Today, Mr Curtis echoed that sentiment.

“In the days following my release on Sunday, I have learned bit by bit that there have  been literally hundreds of people, brave, determined and big-hearted people all over the world working for my release.

"They've been working for two years on this.  I had no idea when I was in prison. I had no idea that so much effort was being expended on my behalf. Now, having found out, I am overwhelmed with emotion."

Mr Curtis said he was grateful for the warm welcome he has received since coming home.

However, Mr Curtis also asked for some time to be alone with his family as he recovered from the ordeal.

He went missing in 2012 and was held by Nusra Front, al-Qaeda's official wing in Syria, whose rivals, the militant group Islamic State, last week killed journalist James Foley.

He arrived in the United States yesterday, according to US media.

He landed in Newark on a flight from Tel Aviv and then flew on to Boston, where he was greeted by his mother, the New York Times reported, citing a family statement.

The comments come against the backdrop of efforts to free other US hostages in Syria.

On Monday, sources familiar with the matter said Qatar, whose diplomacy helped free Mr Curtis, is working to help free four other Americans held hostage in Syria by various armed groups.