Secretary of State John Kerry can't say yet if Middle Eastern Christians are being targeted for genocide because the "first discussion" of the matter reached his desk within the last month.

"I think I only had the first discussion come to my desk in terms of a legal interpretation a couple of weeks ago, and that's when I immediately initiated some re-evaluation, which I'm looking at," Kerry told the House Foreign Affairs Committee chairman on Thursday.

House Democratic and Republican lawmakers have been pressing President Obama's team to describe the Islamic State's slaughter of Christians as a genocide for months. The State Department has been planning to designate the destruction of Yazidi communities in northern Iraq as a genocide since November, but the plight of the Christians in the region has been a source of greater debate.

Kerry offered the insight moments before dubbing "radical religious extremism" the top threat to the United States. "The top threat to the United States today in terms of day-to-day life and the stability of the world, it is violent extremism, radical religious extremism," he said.

That provoked an outburst from Rep. Dana Rohrabacher, R-Calif. "It is disheartening when a representative of our government can't say radical Islamic terrorism and at the same time can't make a decision whether Christians are being targeted for genocide," the lawmaker said. "This is not acceptable."

"I think you heard me say that it is predominantly, predominantly Islamic, and I have no hesitation in saying that," Kerry replied.