The EU leaders have congratulated the victory of the new British Prime Minister Boris Johnson, but the majority of them stressed the challenges that have yet to befall.

Johnson said earlier that the UK should be ready for a breach without a deal

After incumbent Prime Minister, Theresa May resigned in May.

Ursula von der Leyen, who will take over the presidency of the European Commission on November 1, reacted to Johnson's victory during a press conference with the French President Emmanuel Macron.

The Guardian quoted Ursula as saying, "There are many different and difficult issues that we need to deal with together.

These are challenging times in front of us. I think that it is very important to build a strong and good working relationship because we are obliged to deliver something that is good for the people in Europe and the United Kingdom, so I am looking forward to working with him, she said.

The current President of the European Commission, Jean-Claude Juncker congratulated Johnson on the vital success, stating he was eagerly waiting to work with him "in the best possible way".

The European Chief Negotiator for the Brexit, Michel Barnier, said the EU expects to work constructively with the prime minister "when he takes office, to facilitate the ratification of the withdrawal agreement."

Whilst, Charles Michel, the Prime Minister of Belgium, who will become the EU Council President, posted on Twitter: "Important challenges ahead of us, such as Brexit".

In addition, Lithuanian EU Health Commissioner Vytenis Andriukaitis compared Johnson with former Russian President Boris Yeltsin, stating: "There was something in the political work that is similar: many unrealistic promises, ignoring economically reasonable and rational decisions".

A spokeswoman for German Chancellor Angela Merkel announced on Twitter that the Chancellor congratulated Johnson and that she expects to have good co-operation with him.

The French President Emmanuel Macron said he is looking forward to working with Johnson not only on the European topics they share and the ongoing Brexit negotiations but also on international issues, such as the situation in Iran and the international security.

Putin wishes Johnson

Even the Russian President Vladimir Putin applauded the appointment of the new British Prime Minister Boris Johnson and wished him great success, the Kremlin said. "It is in the interest of both countries and nations to develop relations in various spheres," Putin told Johnson, according to The Guardian.

The current relations between Russia and Britain are tense after the poisoning of former Russian spy Sergey Skripal in the British territory.