Media playback is unsupported on your device Media caption May: I want to give EU residents certainty

European leaders have criticised the UK's offer to EU nationals after Brexit - with one senior figure claiming it could "worsen the situation" for them.

European Council President Donald Tusk said the plan was "below expectations" while German Chancellor Angela Merkel said there had been "no breakthrough".

Theresa May conceded there were differences between the two sides.

But the prime minister said those who had "made their lives and homes" in the UK would have their rights guaranteed.

She also suggested that while rights would be enforced by British courts, they could also be enshrined in international law if the agreement was included in the final treaty of withdrawal.

Both the UK and the rest of the EU say they want to come to an arrangement to secure the status of the 3.2 million EU citizens in the UK and the estimated 1.2 million Britons living in EU countries.

Media playback is unsupported on your device Media caption EU chief's one word response to May's plan

Under plans announced on Thursday by Mrs May, the UK envisages giving all EU citizens the right to stay after the UK's exit - due on 30 March 2019 - and granting those resident for at the least five years the same rights to welfare, pensions and education as UK citizens.

However, no cut-off date for the package has been specified by Downing Street and further details of the plans will not be released until Monday.

The offer has received a mixed response from EU leaders with some describing it as a "good start" but calling for more detail.

Speaking at a joint press conference with French president Emmanuel Macron, German Chancellor Angela Merkel said there was a "long way to go".

"That was a good beginning but - and I'm trying to word this very carefully - it was not a breakthrough," she said.

"We don't want a wedge to be driven between us. We do want to make our interests very clear and if there is no guarantee for the full freedoms, then this exercise will have to lead to a situation where there are certain effects on the future relationship between the UK and the 27 member states."

Mr Tusk, who represents the other EU 27 nations, said the EU would "analyse line by line" the UK's proposals when they were published in full but his "first impression is that the UK's offer is below our expectations and that it risks worsening the situation of citizens".

And Joseph Muscat, the prime minister of Malta - who currently holds the rotating presidency of the EU - warned of people being "treated differently" depending on when they arrived in the UK.

Who will police the new rules?

By political editor Laura Kuenssberg

While complex, this summit was perhaps a brief respite from the brooding turmoil in her own party, where questions about the viability of her leadership lurk. Governing is doing, not fending off enemies - and at least today, Theresa May has done that.

There was also a big hint about how the British negotiators hope to get round one of the big obstacles. As we've discussed before one of the big gaps between the two negotiating sides here are who will police the rules on citizen's rights. So, if something goes wrong, who can they appeal to, how will their rights be protected.

The EU side is adamant that it can only be the European Court of Justice. Theresa May has been totally insistent that it can't be them.

At the press conference this afternoon she repeated that it would be the British courts in charge. So far, so the same. But she then tantalisingly - if you are a nerd like me - said that because the rights would be agreed as part of the withdrawal treaty, they would be therefore subject to international law.

Therefore, theoretically, that means they could be enforced by an international court of some variety. Lawyers suggest that is not likely to be the Hague, but could be some kind of new organisation that had British and European lawyers involved. Read more

EU nationals in the UK currently have a right to permanent residence, granted after they have lived in the UK, legally and continuously, for five years.

The European Union has said EU citizens should continue enjoying the same rights as they do now on a lifetime basis, enforceable by the European Court of Justice. But the UK's view is that British courts should have jurisdiction as they will be enshrined in UK law.

Media playback is unsupported on your device Media caption "There are still so many unknowns" on future of EU citizens says ex-Czech Europe Minister

Mrs May said there had been a "very positive" discussion with other EU countries. She acknowledged differences over their enforcement but said she "remained of the view that this is a fair and serious offer".

"Let's be clear about what we're saying. What we're saying is that those citizens from EU countries who have come to the United Kingdom, those EU citizens who have made their lives and homes in the UK will be able to stay and we will guarantee their rights," she said.

The PM said the issue would be one of the first to be discussed and she wanted an agreement as soon as possible.

'Disappointing'

In response to claims by the former chancellor George Osborne, in an article for the Evening Standard, that she had "blocked" calls for the UK to offer a unilateral guarantee of rights in the aftermath of last year's referendum, she said that was "certainly not my recollection" of events.

Anne-Laure Donskoy, founding member of the 3million - which aims to protect the rights of EU citizens living in the UK - said the UK's offer was "disappointing" and "really falls short of our expectations".

"It is like a teaser this statement, it gives you general direction of travel potentially, but there are things in the statement that need to be unpicked."

Labour leader Jeremy Corbyn urged the government to guarantee all UK-based EU citizens full residency rights, saying the current offer "doesn't go far enough and leaves uncertainty for those who have been here for less than five years".

"These are people who are working here and have families here - we have to end their uncertainty."