Theresa May has rebuffed the idea that EU citizens will have the same rights if they arrive in the UK after March 2019.
The UK and the EU are starting negotiations on the so-called transition period, an adjustment phase after Brexit, which is designed to allow businesses and citizens time to adjust to new rules and regulations.
The period is expected to last two years, and has become a subject of contention between the UK and its European peers.
The EU is demanding a "status quo" transition. However, Brexit secretary David Davis has said the UK should be able to sign new trade deals, and the Prime Minister has drawn a red line on immigration, the BBC reported.
"Now for those who come after March 2019, that will be different because they will be coming to a UK that they know will be outside the EU," May said. "This is a matter for negotiation."
The EU and the UK are aiming to agree the terms of the transition period by the end of March, but disputes could create delays. Businesses have said they need certainty over the transition phase in the first quarter of 2018 to avoid triggering contingency plans for a "no deal" Brexit.