Speaking at his general audience on Wednesday, he said that he had followed the news of the attacks in the Belgian capital with an "aching heart", according to Vatican Radio.
Pope Francis has assured families of all victims, as well as those injured or witnesses to the attacks, that his prayers are with them.
Speaking to the audience, he said: "I once again appeal to all people of goodwill to unite in the unanimous condemnation of these cruel abominations that are causing only death, terror and horror."
The pontiff continued: "I ask everyone to persevere in prayer and to ask the Lord in this Holy Week to comfort the hearts afflicted and convert the hearts of these people blinded by this cruel fundamentalism."
He concluded his audience and appealed for prayer by asking the crowd to pray a Hail Mary with him as the crowds prayed in silence.
