LONDON (AP) — Britain and the EU haven't even begun divorce talks but they are already bickering, as political and economic shockwaves from the British vote spread around the world.

Credit rating agency Moody's downgraded the U.K.'s economic outlook from stable to negative, saying Britain faces "a prolonged period of uncertainty ... with negative implications for the country's medium-term growth outlook."

The victorious "leave" campaigners in Thursday's referendum have said there is no rush to trigger Article 50 of the EU's Lisbon treaty, which will begin a two-year exit process to renegotiate trade, business and political links between the U.K. and what will become a 27-nation bloc.

Prime Minister David Cameron, who announced his resignation Friday, said his successor, to be chosen by October, should start the process.

But European Commission president Jean-Claude Juncker said Saturday that the British had voted to leave, and "it doesn't make any sense to wait until October to try and negotiate the terms of their departure."

"I would like to get started immediately," he said.

Juncker said the split was "not an amicable divorce" — adding that it was never "a tight love affair anyway."

The referendum has triggered political and financial turmoil around the world. Stock markets plummeted Friday, with the Dow Jones industrial average dropping 611 points, or 3.4 percent, its biggest fall since August.

The pound dropped to its lowest level since 1985, plunging more than 10 percent from about $1.50 to $1.35 before a slight recovery, on concerns that severing ties with the single market will hurt the U.K. economy and undermine London's position as a global financial center.

Top diplomats from the European Union's six founding nations were meeting in Berlin for hastily arranged talks.

German Foreign Minister Frank-Walter Steinmeier cautioned against rash decisions, saying that "it's totally clear that in times like these one should neither be hysterical nor fall into paralysis."

The vote to leave the EU also caused an earthquake in British politics. The Conservatives are facing a leadership battle to replace Cameron, and some members of the opposition Labour Party also hope to oust their leader, Jeremy Corbyn.

Many Labour lawmakers were strongly pro-"remain" and accuse the socialist Corbyn, a longtime critic of the EU, of failing to rally Labour supporters behind staying in the bloc.

Labour legislator Frank Field said Saturday that Corbyn "clearly isn't the right person to actually lead the party into an election because nobody thinks he will actually win."

"We clearly need somebody who the public think of as an alternative prime minister," Field told BBC radio.

Scottish First Minister Nicola Sturgeon was meeting with her Cabinet in Edinburgh Saturday to discuss the implications of the referendum. A majority of Scots voted to remain in the EU, while most voters in England backed leaving.

Sturgeon, leader of the pro-independence Scottish National Party, said Friday that "Scotland has voted to stay in the EU," and a new referendum on independence from the United Kingdom is now "highly likely." Scotland voted in 2014 to remain a part of the U.K., but that decision was seen by many as conditional on the U.K. remaining in the EU.

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Associated Press writer Kirsten Grieshaber in Berlin contributed to this report.