"What the new set-up means for #Brexit we will have to wait and see", Dutch Prime Minister Mark Rutte said in a tweet.
The decision of Britain to leave was a shocking and cathartic moment in the 60-year history of the bloc, whose member states want to keep Britain as a close partner once it is out.
However, in an official congratulations to May issued later, he said: "Our shared responsibility and urgent task now is to conduct the negotiations on the UK's withdrawal from the European Union in the best possible spirit, securing the least disruptive outcome for our citizens, businesses and countries after March 2019".
May called the snap election in April saying she wanted to increase her majority in order to have a stronger position in Brexit negotiations.
Among Friday's election surprises were the spike in support for the opposition Labur party in London, which voted overwhelmingly to remain in the European Union, and a strong showing for the pro-European Liberal Democrats.
"Looks like it was the Brexit election after all".
"The timeframe set by Article 50 of the Treaty leaves us with no time to lose. But not quite the Brexit election we expected", said Rob Ford, political science professor at Manchester University. Perhaps it would enable her, the optimists suggested, to tack towards a softer, "more realistic" Brexit posture.
"For the next Government, the need and opportunity to deliver an open, competitive and fair post-Brexit economy that works for everyone across all our nations and regions has never been more important".
But the man who hopes to dethrone German Chancellor Angela Merkel in the coming September elections, SDP leader Martin Schulz, congratulated his British counterpart, Jeremy Corbyn, on the night's results.
"We may well be looking down the barrel of a second referendum", he said.
Theresa May was re-appointed UK Prime Minister on Friday, but her Conservative Party lost 13 seats in Friday's snap election, leaving it eight MPs short of a parliamentary majority.
"We want to negotiate quickly, we want to stick to the time plan, and so at this point I don't think there is anything to suggest these negotiations can not start as was agreed". "A vote for one to go and the other to be revisited".
But without the strong mandate Mrs May had hoped for, and with no majority, the UK's strategy for negotiating Brexit has been thrown into uncertainty.
Preliminary results indicate she will instead face a far tougher balancing act between europhiles and eurosceptics within her own party.
A spokesman for Mrs Merkel had previously refused to be drawn on the issue out of "politeness and respect" while the process of forming a new United Kingdom government was under way.