Security in Berlin has been stepped up in Berlin as Germany's capital prepares to welcome the former US President Barack Obama.

Obama is visiting Berlin for the 500th anniversary celebrations of the Reformation.

There will be some minor adjustments to the security arrangements after the Manchester attack, but police had in any case already 'thought through every scenario'.

As many as 140,000 visitors are expected for the special Church Congress, the bi-annual Kirchentag, which begins today and has 2,500 events planned, including an open air service in Martin Luther's home town, Wittenberg.

Events include a debate between Obama and German Chancellor Angela Merkel.

'We've thought through every possible scenario," police spokesman Thomas Neuendorf told Die Welt. There will be some adjustments 'but on the whole, our security concept will stay the same same.'

There will be 4,000 police officers deployed. And for the first time at a Kirchentag, bags will be checked at the doors to all events, including those in churches.

Of the debate between Obama and Merkel, Kirchentag President Christina Aus der Au said: 'The United States is strongly marked by the Reformation and its historical impact. At the same time, the Protestant churches and communities there have developed in their own way. President Obama and Chancellor Merkel have said that their dedication as politicians is also an expression of their Christian faith.

'The Kirchentag movement lives from people who work for justice and solidarity on the basis of their faith. It will be really interesting to hear what the two of them say to us Christians in Europe.'

Other preachers at the celebrations include South African Archbishop of Cape Town, Thabo Makgoba.