British Prime Minister Theresa May (center) prepares for a roundtable meeting at the EU Council headquarters on the second day of a two day European Council summit on June 23, 2017 in Brussels, | Leon Neal/Getty Images EU leaders: Theresa May’s offer on EU citizens is inadequate The prime minister’s proposals received a hostile reaction from EU citizens in the UK.

EU leaders in Brussels gave a skeptical response to the U.K.'s proposals for safeguarding the rights of around 3.2 million EU citizens in the country post-Brexit, with European Commission President Jean-Claude Juncker describing them Friday as a "first step" but not sufficient.

After dinner at the European Council meeting Thursday, Prime Minister Theresa May outlined what she described as a "fair and serious offer" on the key issue of citizens' rights. She told EU leaders that the U.K. did not want anyone to have to leave, “nor does it want families to be split up” — and that she hoped a deal could be done quickly.

Council President Donald Tusk prevented a full discussion on the proposals, which will be released in detail Monday, and EU officials were adamant that the formal Brexit talks process was the right place for negotiations to occur.

The reaction among EU leaders will be concerning to the British who had hoped to get the talks off to a positive start with what had been billed before the U.K.'s general election as a "big and generous" offer on a topic where there is political will on both sides to get a deal.

German Chancellor Angela Merkel declared the talks a good start Thursday but said there was more work to do, a sentiment echoed Friday by Austrian Chancellor Christian Kern. “It’s a good first proposal, which I appreciate, but it’s clear that we have to invest much more work. There are a lot of other citizens who are not covered with Mrs. May’s proposal, and this will be part of the negotiations.” Dutch Prime Minister Mark Rutte, said there were “thousands of questions to ask” about the proposal.

Croatian Prime Minister Andrej Plenković said Friday: “It is one of the key matters in the entire process of negotiations under the Article 50 … It will time to take us some time to reach the final agreement.”

Manfred Weber, who chars the European People's Party group in the European Parliament also expressed concern: "We in the European Parliament will not accept EU citizens being left in uncertainty. It is neither in the U.K.'s, nor in the EU's interest, to have no clear picture. If Prime Minister May cannot come up with a more concrete proposal it is quite worrying for the rest of the negotiations. It still seems that the U.K. government has no idea what they want to achieve."

May’s proposal was met with political hostility back home. Tim Farron, the pro-EU outgoing Liberal Democrat leader, said it leaves too many unanswered questions for citizens. “These proposals are frankly too little too late, and leave millions of people still facing unanswered questions over their futures here. It is simply not good enough.”

Keir Starmer, the opposition Labour party's shadow Brexit secretary, reiterated his party's position that EU citizens should not be treated as bargaining chips in the talks. “We believe there must be a clear commitment that there will be no change to the status of EU nationals in the U.K. This is not only the right thing to do, but it will also help deliver a reciprocal agreement for the 1.2 million U.K. nationals living in the EU.”

EU nationals #citizensrights: EU: comprehensive offer to protect @BritishInEurope

UK Gov: "we won't deport you" Slap in the face! pic.twitter.com/dqJzjDBElv — the3million (@The3Million) June 23, 2017

The 3Million, a group which represents EU citizens living in the U.K., described May's offer as "a slap in the face." It claimed that 29 percent of EU nationals applying for citizenship would not meet the criteria set out by the prime minister. "How callous do you have to be to dress up offer on not deporting family members as a 'generous' offer on EU nationals," the group tweeted.

May will release her official proposal on Monday, giving Brexit negotiators time to digest the document before their next meeting.