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. The FTSE 100 was recently down 0.31% in morning trading after two days of gains.

S&P 500 mini futures were recently down 0.33% and Dow JonesIndustrial Average mini futures were down 0.24%.

Obama said that the government and Federal Reserve were closely monitoring the markets for any indication of systemic strains on the system.

"So far what you have seen are reactions in the market [in] stock prices and currencies. I think the preparations done by central banks and finance ministers ... indicate the degree to which the global economy in the short run will hold steady," he said.

Obama was the latest to warn about the political jockeying taking place in the U.K. and Europe, saying that leaders should conduct exit negotiations in a timely and orderly manner.

He said, "Everyone should catch their breath, come up with a plan and a process that is orderly, that is transparent, that people understand and then proceed in understanding that both sides have a stake in getting this right. It'll be a difficult process."

Yesterday European leaders took a hard line with the U.K. saying they could not pick and choose the aspects of a free market that they would like.