The US State Department has delayed the decision to call the suffering of Christians and other religious minorities in the Middle East genocide.

US Secretary of State John Kerry will not have a decision on whether atrocities committed by Islamic State constitute genocide by a March 17 deadline set by Congress, but he should have a decision soon, the State Department said on Wednesday.

"We are informing Congress today that we're not going to make that deadline," State Department spokesman Mark Toner told a news briefing.

The delay came two days after The House of Representatives voted by 393 to 0 that "the atrocities perpetrated by ISIL against Christians, Yazidis, and other religious and ethnic minorities in Iraq and Syria constitute war crimes, crimes against humanity, and genocide," and weeks after the European Parliament declared the same.

"We certainly respect the deadlines that Congress lays down on specific reports, or in this case decisions about genocide," he said. "However, we also take the process very seriously. And so if we need additional time... in order to reach a more fact-based, evidence-based decision, we're going to ... ask for extra time."

The vote in the House came after the release of a detailed report which documented the persecution faced by Christians in Syria and Iraq at the hands of ISIS, compiled by Knights of Columbus and In Defence of Christians.

"The American people and global conscience implore our national leaders to not stand silent in the face of mounting international consensus. In Defense of Christians asks the Secretary of State John Kerry to speak out soon on behalf of Christians and other minorities undergoing genocide at the hands of ISIS," IDC Executive Director Kirsten Evans said in a statement responding to the delay

"Christians—once one of the largest religious minorities in the region—are losing their lives as the daily targets of ISIS. The images of their beheadings have been broadcast for the world to see. Hundreds of thousands of those who have survived are living as IDPs (internally displaced person) and refugees in foreign lands. Having lost everything, and with little real support from the West, they are being condemned to a future without education, without medical care, without proper shelter, without enough food, without a home. A future without hope," she added.