London (CNN) Britain's Prince Harry has avoided opening up a diplomatic rift between the British and US governments over the guest list for his wedding to Meghan Markle, saying plans had yet to be finalized.

Asked on a BBC radio program whether he would invite former US President Barack Obama Harry swerved the question, saying he didn't want to "ruin that surprise."

There has been speculation in the UK media that British officials fear the political consequences if the couple decide to invite Barack and Michelle Obama, with whom they are friends, but not President Donald Trump.

Markle, an American actor, has been critical of Trump in the past, and there is already widespread controversy in the UK over the prospect of an official visit by the President to the UK.

Then-US President Barack Obama meets with Prince Harry at the White House in October 2015.

The wedding is not a full state occasion and the guest list is being drawn up by Buckingham Palace, with the British government in a consultative role. It is not clear whether Downing Street would insist on Trump or a representative being invited, or whether it could block an invitation being extended to the Obamas.

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