Volodymyr Zelenskyy says there is a "long way to go" to reach the end of the war with Russia.
Speaking to reporters at Stansted Airport, the Ukrainian president says an agreement to end the war needs to be "honest", "fair" and "stable".
"It has to be very specific, very specific security guarantees," he adds.
He says Ukraine is "not talking" about any concessions today, because that would be "wrong" and he is "hearing signals from various partners".
"Ukraine will never recognise territories that are occupied by Russia as Russian territory. For us, this will be temporary occupations," he says.
"Our territories and our values are not for sale. Our freedoms are not for sale. We're paying a high price for the fact Russia has brought this onto us."
Talking about security guarantees, he says he hopes they would make it impossible for Russia to come forward with any other aggression or, if it does, that it will see a "strong response" from Ukraine and others.
"I don't want to talk about the details until there are some signatures... there are too many things to think of," he adds.
"Today, partners have agreed to keep the pressure on."