Global growth could be under threat now that the U.K. has voted to leave the European Union, President Barack Obama has said. Speaking at a press conference in Ottawa, Canada, following a summit with the leaders of Canada and Mexico, Obama said, "There are some genuine longer term concerns for global growth if in fact Brexit goes through." He warned that the implications of lower growth "freezes the possibility of investment in Great Britain or in Europe as a whole at a time when global growth rates were weak already, [Brexit] doesn't help." Markets plunged after the result of the referendum was known last week.