The Rev. Franklin Graham, son of evangelist Billy Graham, questioned the president's religious faith today, saying he was unsure whether Obama was a Christian.

"I think you have to ask President Obama," Graham said when asked on MSNBC's "Morning Joe" whether the president is a Christian. "He has said he's a Christian, so I just have to assume that he is."

While Graham said there was "no question" that Republican presidential candidate Rick Santorum is a man of faith, he doesn't know whether the president is a Christian.

The reverend also declined to say whether he thought Mitt Romney's Mormon faith qualified him as a Christian. "He's a Mormon," he said. "Most Christians would not recognize Mormonism as part of the Christian faith."

The CEO and president of the Billy Graham Evangelistic Association said Obama told him he started attending church only because community groups in Chicago told him he needed to do so to work with them.

"You have to go by what a person says and how they live their life and where they go to church. Are they faithful church-goers? Or do they just go when the cameras are on them," Graham said.

Graham explained his belief that the Muslim world sees Obama as a "son of Islam" because of his father's religious beliefs.

"Under Islamic law, the Muslim world sees Barack Obama as a Muslim. … That's just the way it works," he said. "That's the way they see him. But, of course, he says he didn't grow up that way, he doesn't believe in that, he believes in Jesus Christ, so I accept that."

Graham also raised concerns about the president's dedication to Christians living in Muslim countries, saying Islam has had a "free pass" under the Obama administration.

"[Under] President Obama, the Muslims of the world, he seems to be more concerned about them than the Christians that are being murdered in the Muslim countries. That's what bothers me," he said.

Speaking about his faith recently, the president recalled a meeting with Graham's father in which he prayed with the prominent evangelical leader.

"I've thought about it in the many days since, because I thought about my own spiritual journey, growing up in a household that wasn't particularly religious, going through my own period of doubt and confusion, finding Christ when I wasn't even looking for him so many years ago, possessing so many shortcomings that have been overcome by the simple grace of God," Obama said at the National Prayer Breakfast earlier this month.

"I have fallen on my knees with great regularity since that moment, asking God for guidance not just in my personal life and my Christian walk, but in the life of this nation and in the values that hold us together and keep us strong," the president added.