HANGZHOU (Reuters) - British Prime Minister Theresa May said on Sunday (Sept 4) that she had discussed Britain leaving the European Union with United States President Barack Obama, and will consult on how the make sure the two countries have the closest possible trading relationship.

The two were meeting on the sidelines of the Group of 20 summit in the eastern Chinese city of Hangzhou, where global leaders are convening.

At a joint news conference, Mr Obama said on Sunday that Mrs May was a steady influence during a time of transition, and that the United States had every intention of ensuring the US-Britain relationship continues post-Brexit.

Mr Obama also said the US would continue to work with Britain on cyber threats, the Islamic State in Iraq and Syria (ISIS) and Ukraine.

On his talks with his Chinese counterpart Xi Jinping a day earlier, Mr Obama said they had been "extremely productive" and that the significance of a row between US and Chinese officials at the airport upon his arrival shouldn't be overblown.

"I wouldn't overcrank the significance" of tensions at the airport, he told a news conference.

Mr Obama's last scheduled trip to China before leaving office got off to an awkward start soon after Air Force One landed in Hangzhou when a Chinese security official blocked National Security Adviser Susan Rice on the tarmac and yelled at another US official trying to help journalists get closer to Mr Obama.

On Russia, Mr Obama said talks will be key in reaching any deal to end hostilities in Syria, but negotiations are difficult and grave differences remain between Washington and Moscow.

The United States has long been interested in finding a way to reduce violence and improve humanitarian aid in Syria but it would be difficult to get to the next phase if there is no buy-in from Russia, Mr Obama said.