Almost 20,000 people marched through Vienna yesterday in protest at the ill-treatment of refugees.

Demonstrators of all ages held up signs reading "refugees welcome" and "I don't want Europe to be a mass grave." Large parts of the city centre had to be closed as the rally moved slowly through the capital, the Guardian reported.

"Say it loud, say it clear, refugees are welcome here," the crowd chanted as they marched towards the Austrian parliament. Police officers removed their helmets as they watched from the sidelines.

At the same time as the march, a service for the dead was held in St Stephen's Cathedral.

"We've had enough – enough of the deaths, the suffering and the persecution," the archbishop of Vienna, Cardinal Christoph Schoenborn, told the congregation, which included senior government members.

The suffocated bodies of 71 people, thought to be Syrian refugees, were found in an abandoned refrigerated truck in Austria last week. Four children were among the dead. It was "too awful" to think of the plight of those in the truck, Cardinal Schoenborn said.

The march in Vienna came after Pope Francis used his Sunday address in St Peter's Square to condemn the treatment of refugees. The deaths "offend the entire human family," he said.

Pope Francis asked the crowd gathered to pray for "all these brothers and sisters" who have died.

More than 2,500 people have died trying to reach Europe so far in 2015, according to the UNHCR. Thousands of Christians fleeing persecution in Iraq, Syria and Nigeria are amongst the huge numbers of refugees seeking safety in Europe.