Owen Smith has cancelled the planned launch of his Labour leadership campaign in the wake of the Nice terror attack.
At least 84 people have died after a lorry was driven through crowds celebrating Bastille Day in Nice.
Mr Smith was scheduled to launch his bid to be Labour leader with an event in his Pontypridd constituency today.
But the former shadow work and pensions secretary, who is challenging Angela Eagle and incumbent Jeremy Corbyn for the Labour leadership, tweeted that the event has now been called off.
He said: "In light of the heartbreaking news from Nice, I am cancelling today's campaign launch. Solidarite et fraternite avec le peuple Francais."
Mr Smith was due to warn that he believes the Labour Party is heading for a "disastrous split".
He was due to say: "This is a moment of deep peril for Labour, if we carry on as we are the party I love will end up in a disastrous spilt. I am not prepared to let that happen.
"The Labour Party must pull through this crisis and unite. We owe it to the millions of people across Britain who look to the Labour Party to provide hope and optimism for their lives."
Angela Eagle has already launched her campaign to try to replace Jeremy Corbyn as Labour leader.
Mr Smith was also due to say that he believes he is the only candidate that can unite the party, which has been rocked by turmoil in recent weeks.
He was going to say: "So now it falls to a new generation of Labour MPs to step forward and secure Labour's future. I am the only person in this race that can do that.
"It's not enough just to talk about being anti-austerity. Labour needs to set out the details of how we overcome Tory austerity and secure the next Labour government that delivers investment, not cuts.
"That's what I will be doing throughout this campaign; setting out the vision and policies that can unite the party and lead us into government."
