Vatican City (AFP) - War is not the way to address injustice, Pope Francis said Sunday, in comments that appeared to distance himself further from any faith-based justification for US airstrikes in Iraq.

"War is never a satisfactory way to right injustices," the pontiff said in a message to an inter-faith colloqium being hosted in Antwerp, Belgium by the St Egido community.

"War leads people into a spiral of violence which becomes difficult to control. It destroys what it has taken generations to establish and leads the way to even worse conflicts and injustices."

The Vatican had last month seemed to endorse airstrikes against the Islamic State, described as "perhaps necessary" by the Holy See's representative at the United Nations.

Shortly afterwards the pope's own remarks in a press conference caused confusion about what the church's stance was.

Asked specifically if he could back US strikes in Iraq to help protect Christians there, Francis replied: "In these cases where there is an unjust aggression, I can only say this: It is licit to stop the unjust aggressor."

He qualified his comment however by adding: "I underline the verb: stop. I do not say bomb, make war, I say stop by some means. With what means can they be stopped? These have to be evaluated. To stop the unjust aggressor is licit."