Foreign and Commonwealth Office minister Tobias Ellwood has met some of the the Iraqi Christian community in London.
He discussed reports from the city of Mosul that ISIS fighters had issued an ultimatum to convert to Islam, pay a tax or face death.
He said: "[I] heard at first-hand some of the appalling reports from Mosul about the threats to Christians by ISIL, leading to many leaving the city which has been the home of Christians for over 1,800 years. This is the latest example of the brutality and intolerance of this group, which has claimed responsibility for numerous atrocities in Iraq and Syria."
It's thought there are now only 10 Christian families left in the entire city after ISIS over took large parts of Iraq.
Thousands of people have been forced to flee to refugee camps and earlier this week France offered some of the asylum.
Mr Ellwood said: "We strongly condemn the persecution of Christians and other minorities on the basis of their religion or belief or ethnicity. The burning of churches and branding of homes is reprehensible, as is the destruction of mosques and desecration of holy sites."
The minister also confirmed the UK government was giving £5 million in humanitarian aid to Iraq.