Barack Obama has distanced himself from Jimmy Carter, the former US president, who plans to meet Khaled Meshal, the leader of Hamas, the radical Palestinian party, in Syria next week.

Mr Obama, who has come under fire from Hillary Clinton for promising to meet hostile leaders – including Mahmoud Ahmadi-Nejad, the president of Iran, and Hugo Chávez of Venezuela – if he is elected, said he drew the line at Mr Meshal.