LONDON – European Commission President Jean-Claude Juncker said on Wednesday he told Prime Minister Theresa May that EU negotiators were “not in a hostile mood” toward Britain but that Brexit talks would be “very, very, very” difficult.

The EU chief executive told a news conference that he had spoken to May on Tuesday after she outlined her plans for leaving the European Union and welcomed the clarity she gave. He said EU negotiators would seek a fair deal for both sides.

“For my part, I will do everything so that the negotiations reach a balanced solution, with full respect for our rules,” Juncker said.

“I welcome the clarifications given by Mrs May, but I said to her last night that a speech will not launch the negotiations,” he said, adding that could only happen when Britain triggers formal divorce proceedings.

“There will be an unprecedented negotiation which must finish within two years and the consequences will be considerable for the United Kingdom, its 27 partners and the whole union.”

In her speech, May vowed to remain a "best friend" to the EU but confirmed that Britain would pursue a clean break from the 28-nation bloc, commonly referred to as "hard Brexit." This will entail leaving both the single market and customs union, breaking away from the European Court of Justice (ECJ), and acquiring full control over the immigration of EU citizens to the UK.

The prime minister also warned that Britain would walk away from negotiations without a deal in place if the terms offered by the EU are unsatisfactory. She said: "no deal for Britain is better than a bad deal for Britain."

The Conservative Party leader's landmark speech received a mixed reaction from politicians across the continent.

Maltese Prime Minister Joseph Muscat, whose government holds the rotating presidency of EU councils, was asked at the same news conference if he heard a threat in May's warning that EU measures to penalize Britain would damage the EU. He told journalists that he had not heard a "declaration of war." European Commission Vice-President Frans Timmermans told Sky's Ed Conway that he was "surprised" by the "positive tone" of May's speech.

However, Guy Verhofstadt, the EU Parliament's chief Brexit negotiator, was not as accommodating in his response. The former Belgian prime minister tweeted that the UK's days of "cherry-picking" were over and condemned May for threatening to turn Britain into a tax haven if it isn't given the level of access it wants to the single market.