The family of Steven Sotloff, the second American journalist beheaded by Islamic State militants, said on Wednesday he was "a gentle soul", and challenged the group's leader to a debate on the peaceful teachings of the Muslim holy book, the Koran.

Family spokesperson Barak Barfi ended the statement with off-the-cuff remarks in Arabic, saying "Steve died a martyr for the sake of God."

He then challenged Islamic State leader Abu Bakr al-Baghdadi to debate Islam, saying, "Woe to you. You said the month of Ramadan is the month of mercy. Where is your mercy?"

"Abu Bakr, I am ready to debate with you. I come in peace. I have no sword in my hand and I am ready for your answer," added Barfi, who is an Arabic scholar and research fellow at the New America Foundation think tank in Washington.

Islamic State released a video on Tuesday (September 2) purporting to show the beheading Sotloff, raising the stakes in its confrontation with Washington over US air strikes in Iraq.

Following the beheading of journalist Jim Foley last week, Sotloff's mother made an emotional plea to Islamic State, requesting they release her son.

The Sotloff family has yet to speak personally to media following their son Steven's death and requested to mourn privately.

US and British officials both examined the video, showing the same British-accented executioner who appeared in an Aug. 19 video of the killing of US journalist James Foley, concluding it was authentic.

The United States resumed air strikes in Iraq in August for the first time since the pullout of US troops in 2011 and Obama said the strikes are already proving effective.

The White House said late on Tuesday (September 2) that Obama was sending three top officials -- Secretary of State John Kerry, Defense Secretary Chuck Hagel and counterterrorism adviser Lisa Monaco -- to the Middle East "in the near-term to build a stronger regional partnership" against Islamic State militants.

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