Europe's Budget Commissioner has warned that a weakened Government in London could undermine the Brexit process.
Gunther Oettinger told German radio station Deutschlandfunk that in negotiations, "a weaker partner weakens the whole thing".
If both sides in a negotiation were strong, "you get results more quickly", he said.
Mr Oettinger said that the European Union was ready for Brexit talks which are due to begin on June 19, and would be "hard but fair" in its negotiations with the UK.
But he warned that time was running out to reach an agreement which could be approved by all 27 remaining governments within the two-year deadline set out in Article 50 of the EU treaties.
Theresa May's decision to hold a snap election had delayed matters, he said, adding: "There is only 15 or 16 months left."
Mr Oettinger said that he did not believe that voters made their decision on the basis of Brexit, as Mrs May hoped.
"It was about social justice and security," he said.
Czech prime minister Bohuslav Sobotka said he was "delighted" that Jeremy Corbyn had significantly strengthened his party's position, saying that the Labour leader was "the real winner of the British election".
Mr Sobotka said that Europe would now have to wait for the formation of a UK Government, but said he did not expect it to take long.
"Britain launched Brexit in March," he said in a tweet. "We only have two years."
An article on the Europe edition of website Politico, which covers the politics of the European Union, said that Britain was waking up on Friday morning "more divided and uncertain about its future than anyone thought possible".
The article by Tom McTague added: "From a position of relative strength, dominating a compliant parliament which had accepted Brexit, Theresa May is now struggling to cling on to her job, unsure whether she will even be able to form a minority government."
The article said Mrs May is "mortally wounded" and looked ahead to who could potentially emerge from the political wreckage, saying: "Boris Johnson is the most obvious Tory winner from the fallout.
"When a steady but uninspiring leader has been found wanting, they may turn to a tried and tested winner with the charisma to take on Corbyn."
Manfred Weber, chairman of the European People's Party (EPP), the largest grouping in the European Parliament, said Britain looked disorientated by the election result.
The German MEP told BBC Radio 4's Today programme: "One year after the decision by the British people to leave the European Union, we see that Europe, Paris for example, Berlin and even Brussels is very stable, so we are ready, and we see disorientation in London, which is not a positive thing."
Asked whether he expected to negotiate with Theresa May, he said it was purely a domestic matter, adding: "We want to start, the time is running, and instability, losing time, is not in your or our interest.
"Europe is for the moment strong and united and we are waiting for Britain."