US President Barack Obama and British Prime Minister Theresa May, at their first meeting since the latter's assumption of office, downplayed concerns about bilateral trade following Britain's decision to leave the European Union (EU).

"The bottom line is we don't have a stronger partner in the world than the United Kingdom," said Obama at the meeting, which took place in this eastern Chinese city on the sidelines of the 11th Group of 20 (G20) summit.

"And despite the turbulence of the political events over the last several months, we have every intention of making sure that continues," he added, referring to Britain's shock Brexit referendum in June.

Washington ruffled London's feathers when it warned ahead of the vote that the United States would prioritize its trade talks with the EU over those with Britain should the latter choose to exit the bloc.

On Sunday, Obama toned down the rhetoric, saying that the warning was never intended to be a punishment. Yet he added that it would not make sense for Washington to deviate from the EU track.

The top priority for London now, Obama said, is to define its new trading relationship with other European countries.

May, for her part, joined Obama in underscoring the two partners' solidarity, pledging that her country will strive to pursue an aggressive trade link with the United States despite the Brexit.

In an attempt to dispel any doubt about whether her country is really leaving the EU, the prime minister ruled out the possibility of holding a second referendum on the EU exit.

"The UK will indeed be leaving the European Union," she said.

On the margins of the G20 summit, Obama also touched upon the Syria crisis, saying that his country and Russia are working around the clock to clinch a deal on how to deal with the situation in the war-torn Middle East country.

Acknowledging that the two countries still have "grave differences," he said, "There is the possibility at least for us to make some progress."