Prime Minister Theresa May said the UK's position on Gibraltar has not changed and she would always "stand by" its citizens ahead of the Brexit summit in Brussels.
Speaking after a meeting with President of the European Commission Jean-Claude Juncker, May said she will always negotiate on behalf of the whole of the UK family.
May said the UK has ensured Gibraltar is "covered by the whole withdrawal agreement" and position on the sovereignty of Gibraltar "has not changed and will not change".
The Prime Minister will now meet with President of the European Council Donald Tusk ahead of the summit.
The meeting of EU leaders is set to go ahead on Sunday after the UK and Spain reached a deal over the issue of Gibraltar.
Speaking in Brussels, Theresa May said: "We have worked through the withdrawal issues for Gibraltar with Spain in a constructive and sensible way and I would like to pay tribute to the statesmanship with which Fabian Picardo has led the negotiations on behalf of Gibraltar.
"We have ensured that Gibraltar is covered by the whole Withdrawal Agreement and by the implementation period and we will always negotiate on behalf of the whole UK family, including Gibraltar, and in the future relationship we will stand up for their interests.
"The UK's position on the sovereignty of Gibraltar has not changed and will not change. I am proud that Gibraltar is British and I will always stand by Gibraltar."
Gibraltar's government said: "The deep and unbreakable bonds that bind the United Kingdom and Gibraltar together have not been in any way, and will not be in any way, diluted as a result of our common departure from the EU.
"Brexit will have no effect on the British sovereignty of Gibraltar and the waters that surround it."
Chief Minister Fabian Picardo added: "'Throughout our history, we've stuck with Britain. After Brexit, we will stick with Britain in the future too.
"This is our most important relationship. And as the UK establishes new trading relationships around the world, we look forward to the opportunities that will come from the benefits of our common language, our common law and the ties that bind us with the Commonwealth of nations around the world."
