The president and former presidents of the Southern Baptist Convention (SBC) have called on President Obama to take "the necessary action" against ISIS, telling him he is in position "for such a time as this".

President Ronnie Floyd, together with 16 former SBC presidents, described ISIS as "a continuing threat to world peace in a way unknown to us since the Nazis of World War II" in an open letter to Obama on March 1.

The letter follows a week in which more than 220 Assyrian Christians were captured by ISIS.

"The abuse, brutalization, and murder of children, women, and men that is occurring before the world calls our country to lead forward to bring this to an end," the church leaders wrote.

The letter called on him to work to protect the vulnerable and assured him of support and prayers from the vast majority of America's largest Protestant denomination.

"The world will applaud your courage and compassion as you defend those that Scripture calls 'the least of these,'" they wrote.

The letter also included an exhortation from the biblical story of Esther.

"Mr. President, just as Esther led forward for the deliverance of the Jews in her day, we believe you also 'have come to the kingdom for such a time as this.' You have been given an historical moment to lead in protecting the people and the principle of religious freedom in the world."

In February Floyd said at a meeting of SBC's executive committee that Christians have a responsibility to speak out against the threat of ISIS, the Baptist Press reports.

At the event Floyd also emphasised the importance of learning from history. "As followers of Jesus Christ, if we do not choose to stand right now and speak up and challenge our nation's leaders – challenge our business leaders to stand up, challenge our churches to stand up, challenge our political leaders to stand up, challenge our state leaders to stand up and every person in America to decry this tragedy," Floyd said "we are just like those who turned their heads in World War II when six million Jews were being killed, or they turned their heads in the 50s and 60s and 70s when African American brothers and sisters and their churches were burned and persecuted and discriminated against all because of the colour of their skin."

He added: "we cannot turn our heads again."