The Vatican's ambassador in Geneva has said the use of force will be necessary to protect minority groups from Islamic State aggression if a political solution cannot be achieved.

In an interview with US Catholic website Crux, Archbishop Silvano Tomasi said the jihadists, who have declared a cross-border caliphate after seizing land in eastern Syria and northern Iraq, were committing "genocide" and must be stopped.

"What's needed is a coordinated and well-thought-out coalition to do everything possible to achieve a political settlement without violence," Crux quoted Tomasi as saying on Friday, "but if that's not possible, then the use of force will be necessary."

Tomasi's words follow repeated condemnations of Islamic State by Pope Francis, who decried the beheading of 21 Egyptian Coptic Christians in Libya in February and has said it is "lawful" to stop an unjust aggressor.

The ambassador's comments were published on the same day a group of countries led by the Holy See, Russia and Lebanon issued a statement calling on the international community to support all ethnic and religious communities in the Middle East.

The Vatican said more than 60 countries including the United States have endorsed the statement, which warns that Christians in particular now "live a serious existential threat".

Tomasi emphasised in the interview that Christians are not the only minority group the Vatican wants to protect from Islamic State, which has beheaded Arab and western hostages and kidnapped or killed members of different religious minorities.

"Christians, Yazidis, Shi'ites, Sunnis, Alawites, all are human beings whose rights deserve to be protected," he said. "Christians are a special target at this moment, but we want to help them without excluding anyone."

Tomasi said any anti-Islamic State coalition should include the Muslim states of the Middle East and be guided by the United Nations.