The installation of a new pope is planned to take place towards the end of next week, when US President Barack Obama is due to make a 48-hour trip to Israel.
Two of the papal candidates - the Archbishops of New York and Boston - are American. If an American pope were to be elected for the first time in history, commentators have suggested that Mr Obama would most likely feel obliged to attend.
There are 75 million Catholics in the US.
