Speaking at the G20 Summit, Obama said the priority was to complete two landmark trade deals - the Trans-Pacific Partnership agreement between the US and Asia and the Transatlantic Trade and Investment Partnership between the US and the EU.
"We're going to do everything we can to make sure that the consequences of the decision don't end up unravelling what is already a very strong and robust economic relationship," said Obama in China on Sunday morning.
"First things first - the first task (for Britain) is going to be figuring out what Brexit means with respect to Europe, and our first task is making sure we get, first, TPP (Trans-Pacific Partnership) done and also that we move forward on the TTIP (Transatlantic Trade and Investment Partnership) negotiations in which we've invested a lot of time and effort."
Obama and Prime Minister Theresa May are meeting for the first time since Brexit at the summit, after the President controversially warned before June's referendum on membership of the EU that Britain would be at "the back of the queue" in negotiating a free trade deal with the US.
In a speech at the leaders' summit Obama said: "It is absolutely true that I believed pre-Brexit vote, and continued to believe post-Brexit vote, that the world benefited enormously from the United Kingdom's participation in the EU."
"What I committed to Theresa is that we will consult closely with her as she and her government move forward with Brexit negotiations to ensure that we don't see adverse effects in the trade and commercial relationship between the United States and the United Kingdom," he added.
May said the meeting between the world's top leaders would be an opportunity for the UK to begin forging new deals post-Brexit.
Ahead of the meeting, she said: "We are going to make a success of Brexit and one way we will do that is by playing to Britain’s strengths as a great trading nation and forging our own new trade deals around the world."
"We are building up the necessary expertise to go after these trade deals and here in China, I will be seizing the opportunity to talk to leaders from countries like Australia who have already made clear that they want to strike a deal once we have left the EU."
Talks will begin this week between the UK and Australia, while the government said New Zealand and Canada had offered the UK help with negotiating trade deals.
May's Australian conunterpart Malcolm Turnbull was one of the first world leaders to indicate a desire to negotiate new trade deals post-Brexit.
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