US Secretary of State John Kerry said Tuesday that Washington will insist strongly that the EU and Britain keep close ties after their Brexit divorce.

"Let me underscore: the United States will support its friends and allies on both sides of the Channel as you work through the tough issues ahead," Kerry said during a speech in Brussels.

"But we will not be shy about where our interests lie: we need the strongest possible EU, the strongest possible UK and a highly integrated, collaborative relationship between them," he added.

Kerry spoke days after British Prime Minister Theresa May announced that her government would start the process of leaving the EU within the next six months.

Fears are growing that May will lead Britain towards a so-called "hard Brexit" -- with London severing ties with the EU's single market and turning its back on Europe.

Growing talk of a hard Brexit sent the pound to a 31-year low against the US dollar Tuesday.

Kerry said: "Our goal, as talks are launched next spring, must be to once again prove the pundits wrong -- to put to shame all those who once again have declared the vision of Europe dead."

The goal was to "reject the new conventional wisdom that the time has come to raise drawbridges to separate countries instead of building bridges to connect countries," he said.