Tens of thousands of European Union supporters gathered in London on Saturday to show their rejection of Brexit and demand a second referendum.

Days before Prime Minister Theresa May is expected to trigger the article that will begin the divorce process between the United Kingdom and EU, the organization Unite for Europe organized a march from iconic points in the city to Westminster Palace, where the British Parliament is located.

Carrying placards painted with clever slogans _ such as "I wanna be inside EU" _ and waving European flags, the participants gave the march a festive atmosphere that was bolstered by the clear skies and warm weather.

Some wanted to express more somber feelings; one teen was seen carrying a sign that said "I'm 15, Brexit stole my future!" reminding crowds that many people opposed to Brexit felt they had been robbed of a chance to flourish within the European community.

Among the marchers were several political figures, including leader of the Liberal Democrats Tim Farron, who demanded that people get a chance to vote on a second referendum that would dictate the terms of the break with Europe.

"We are not giving up this week of all weeks. We here are as testament that we refuse to despair. Britain can be better," he told the crowds.

The London event was held in the midst of increased security measures as only three days earlier, Westminster was the site of a terror attack that left five people, including the assailant, dead.

A similar march was organized in Edinburgh, where the Young European Movement gathered to show their support for the EU, in a region where the vote to stay within the bloc overwhelmingly won.

Scottish First Minister Nicola Sturgeon is now fighting for a chance to hold an independence referendum that would break Scotland away from the UK but might give it a chance to remain in the EU.

The marches coincided with the Rome Summit, where the heads of state and government of 27 EU member countries _ excluding the UK _ gathered to commemorate the 60th anniversary of the Treaty of Rome, which led to the foundation of the EU.

The leaders took the opportunity to sign the Rome Declaration, which outlines the bloc's plans for meeting the main challenges it faces today.