Archbishop Silvani Tomasi said the international community must do more for religious minorities being persecuted in Iraq.
He told Vatican Radio: "At this moment, the Holy Father, Pope Francis, and other members of the Christian community, including the World Council of Churches, are taking a strong stand in defence [of the Iraqi Christians] and their right to survive and to live in peace in their own home, which for the last 2,000 years has seen them active and contributing to the development of the region.
"However, we are faced with a certain indifference at the practical level with the international community. It is difficult to convince—because of false modesty, I would say—the Western powers to take a strong stance in defence of the Christians.
"At this moment, we hope the voice that is surging from different Christian and religious communities, from moderate Muslims, from people of good will around the world, may find the response of concrete humanitarian assistance that is provided for the Christians in northern Iraq as well as some political and even effective military protection."
Islamic State (IS) fighters, formerly ISIS, have forced tens of thousands of Christians to flee their homes as they take over parts of Iraq.
Last week the US president Barack Obama said American forces would carry out strikes on the extremists to stop them advancing any further.
Mr Obama also said aid would be dropped to help those fleeing the militants.
The UK Government has confirmed it will also drop supplies but Downing Street has ruled out any military intervention and recalling parliament.
Thousands of Christians were forced to flee their homes in the town of Qaraqosh last week after IS militants stormed the area.
Some have taken refuge at a church in the town of Ankawa near Irbil.
It's providing food, water, medicine and tents but is already seriously overcrowded.
Meanwhile British forces have dropped a second round of aid to people trapped on a mountain in northern Iraq after fleeing Islamist militants.
The RAF says it was able to deliver essential supplies including reusable water purification containers and solar lamps.
The first aid drop took place over the weekend.
The UK's also looking into getting equipment to Kurdish forces fighting I.S. militants - while the U.S. has "stepped up" its support.
State Department spokesperson Marie Harf says America will work with the Iraqis: "Whether that's providing intelligence, whether that's providing arms and weapons and missiles - we've been doing all of that.
"But there's no long term American military solution here, the Iraqis need to get back on their feet, we're helping them do that, and they need to put in place a way to eventually fight this threat themselves."