The UK is to fund £16.5 million of warm clothing, tents, blankets, heaters and other winter supplies for Iraqis facing bleak sub-zero conditions after being forced to flee their homes from Islamic extremists.

At least 2.1 million people have been displaced since January according to United Nations estimates and International Development Secretary Justine Greening urged other countries to increase their emergency funding.

"ISIL has brutally and indiscriminately murdered and driven out Christians, Yazidis and Muslims alike across Iraq," she said.

"As winter takes hold, temperatures will plummet and thousands of women, children and other vulnerable Iraqis face bitter conditions with no protection from blizzards and flooding.

"The UK is providing essential, lifesaving winter supplies. Others must now urgently follow suit, before the worst of the winter weather takes hold."

The support, which takes the total UK commitment so far to £39.5m, will be delivered through agencies such as UNHCR and the International Organisation for Migration (IOM).

It is expected to pay for blankets, heating stoves and other cold-weather supplies for 14,000 vulnerable families, cash and vouchers to help 16,000 families buy winter gear and to deliver improved shelter for another 4,500 families.