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An American man killed fighting alongside Kurdish forces against ISIS believed it was "God's will" that he go to Syria, his mother told NBC News.

"I didn't want him to go but I didn't have a choice in the matter," Keith Broomfield's mother, Donna, tearfully said in a phone interview Wednesday from Westminster, Massachusetts.

A woman who identified herself as Keith Broomfield's sister posted a text-message exchange on her Facebook page in which he explained his reasons for going overseas.

"I'm gonna do what I got to do," he wrote. "Sometimes you got to be a man whether you want to or not. I don't expect anyone to understand but I don't need anyone to either.'

A State Department official confirmed to NBC News that Broomfield, 36, was killed in Syria. The official did not provide further details, saying only that the State Department was in touch with his family.

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Twitter accounts and Facebook pages linked to Kurdish fighters were first to report his death, calling Broomfield a "martyr" and saying he was killed in the Syrian countryside surrounding Kobani. There was no immediate official confirmation from the secular Kurdish forces fighting ISIS in Syria known known as the YPG.

Idris Nassan, Kurdish co-deputy foreign minister of the Kobani district, also confirmed to NBC News that an American who had joined Kurdish fighters died in a battle with ISIS in his area. It was not immediately clear when Broomfield was killed.

Donna Broomfield said that her son — who had been the production manager for the family's manufacturing firm —had left to join the Kurds about four months ago.

“He turned his life over to the Lord and he decided this was God's will and God wanted him to do it," she said.

There was "a little bit of texting" after he first arrived, but lately she had heard "nothing."

"I’m waiting for his body to come back,” she added.

Jennifer Broomfield, who posted the text messages on Facebook but could not be reached for comment, wrote on her page that she "didn't think she would lose him."

"If we allow this war to continue we are ignoring that we are all sisters and brothers," she wrote.

"My brother died to defend my sisters who are being sold, enslaved, raped and murdered. To defend my brothers who are shot beheaded and dumped into piles off trucks.