The systematic murder of Christians and other religious minorities in the Middle East cannot be labelled a "genocide" until an "additional evaluation" has been done.

This is according to US Secretary of State John Kerry who told Congressman Jeff Fortenberry he was considering the matter after the Nebraska representative tabled a resolution for Congress to recognise the killings as a genocide.

"I will make a decision on it as soon as I have that additional evaluation and we will proceed forward from there," said Kerry.

Fortenberry's resolution expresses "the sense of Congress that those who commit or support atrocities against Christians and other ethnic and religious minorities, including Yezidis, Turkmen, Sabea-Mandeans, Kaka'e, and Kurds, and who target them specifically for ethnic or religious reasons, are committing, and are hereby declared to be committing, 'war crimes,' 'crimes against humanity,' and 'genocide.'"

The move comes after the European Parliament unanimously passed a motion on February 4 to acknowledge continued slaughter of minorities as genocide. It is the first time the body has recognised an ongoing conflict as genocide.

The term carries significance because of the obligations it places on states to intervene. Pressure is mounting on the US to follow the European Parliament's motion.

"We are currently doing what I have to do, which is review very carefully the legal standards and precedents for whatever judgment is made," Kerry said in response to Fortenberry.

"I can tell you we are doing that. I have had some initial recommendations made to me. I have asked for some further evaluation. And I will make a decision on this."

An early day motion (EDM) has also been tabled in the British parliament to recognise the killings as genocide. It is been signed by 50 MPs so far, including a number of Christian MPs who sponsored the motion. However EDMs are not binding on the government and it is unlikely action will result.