The Italian prime minister has branded the UK's Brexit vote a "bad decision" and blamed it on former PM David Cameron.
Matteo Renzi also suggested the UK will not be able to have full access to the single market while curbing immigration, saying it will be "impossible" for British people to have more rights than others outside the EU.
His comments come as former education secretary and Remain campaigner Nicky Morgan criticised the British government's "lack of a plan" and urged Theresa May to come up with a clear strategy in the next couple of months.
Speaking to the BBC, Mr Renzi (pictured below) said he was "shocked" when Britain voted to leave the EU but agreed that "Brexit is Brexit - the people of the UK decide the way for the future".
He said he "tried" to keep the UK in the EU, but blamed Brexit on Mr Cameron's decision to hold a referendum to solve his own internal party problems.
He said: "The problem was one problem. When David Cameron decided to use the referendum to solve the internal problems of the Conservative Party, this was the problem. We cannot use foreign affairs to solve internal problems.
"The decision of (the) British people is a bad decision in my mind and I'm sad for that, but if we don't accept the result of the referendum the risk is we give the message that a vote is not a good thing, democracy is not an asset for this continent."
He said he is ready to negotiate with Mrs May once she triggers Article 50 and starts formal talks on Britain's departure from the EU.
He added: "But it will be impossible to give British people more rights than the other people outside the EU."
Asked if there could be some "flexibility" over the EU's rules over freedom of movement and access to the the single market, he said: "This is a very interesting debate because this debate will be a debate about the concept of rules in the EU. But when the UK decides the opening of Article 50 we will discuss about this."
He urged Mrs May to trigger Article 50 "as soon as possible". Mr Renzi also stressed that he wants Britain and the EU to have a strong relationship following Brexit. He said: "Now the situation is that we can and we have to build the best alliance between the UK and the EU for the future because we will be best friends for the next years."