At least 84 people, including around a dozen children, were killed when a terrorist drove a truck through crowds celebrating Bastille Day in Nice.
In a tweet the leader of the Church of England said we must "weep with them" and "stand with them".
Elsewhere US president Barack Obama said his "thoughts and prayers" were with the loved ones of those killed and wished those wounded a full recovery.
The new Environment Secretary and committed Christian Andrea Leadsom tweeted: "Terrible and tragic news from Nice today - all thoughts and prayers with those affected, and the people of France."
The Church of England's Bishop in Europe Rt Revd Robert Innes called it a "terrible event" that reminds us to stand together in the face of violence.
He said: "I continue to pray for peace and, today in particular, we hold in our prayers the victims of this attack and their families."
Catholic Primate of All Ireland Archbishop Eamon Martin asked for prayers for those killed and injured.
"The horrific scenes on the streets of Nice once more send shock waves into our homes and hearts. How helpless we all are when someone decides to deliberately and indiscriminately target human life," he said.
