More than 150 monuments and buildings across Europe will be lit up blue on Saturday to mark the 75th anniversary of the United Nations.
The UN's Palais des Nations headquarters in Geneva, the Grand Place in Brussels, and Dublin Castle were among the locations set to turn the shade of blue used on the UN flag.
The United Nations officially came into existence on October 24, 1945, when the UN Charter, agreed four months earlier, came into force.
Starting out with 51 original members, there are now 193, with South Sudan the latest to join in 2011.
"The United Nations has spanned the decades helping millions of people to escape the yoke of poverty, gain access to education and health, have their fundamental rights respected, and enjoy better livelihoods," it said in a statement.
"It also helped the world avoid a third world conflict -- the main reason it was created -- and remain relatively peaceful."
Locations turning blue included the city halls in Barcelona, Belfast and Copenhagen; cathedrals in Stockholm and Reykjavik; the Jet d'Eau fountain in Geneva; the bridges of Turin; the Peace Palace in The Hague, and the Presidential Palace in Bratislava.
The Foreign Office in London, the UNESCO headquarters in Paris, Rua Augusta Arch in Lisbon, the Olympic Museum in Lausanne, Mostar Bridge in Bosnia and Herzegovina, the Zizkov Television Tower in Prague and Ljubljana's Triple Bridge were also to be lit.
UN chief's ceasefire call
In a speech in New York marking the anniversary, UN Secretary-General Antonio Guterres said international solidarity was urgently needed in unprecedented times as the coronavirus pandemic sweeps the globe.
"On United Nations Day, I reinforce my appeal for a global ceasefire so we can devote all our energies to fighting Covid-19," Guterres said.
"Let us act together now to defeat the pandemic, prevent climate catastrophe, uphold the equality of women and men and pave the way for a safer, healthier, more just and sustainable world."
The United Nations officially began once the UN Charter had been ratified by Britain, China, France, the Soviet Union and the United States, and by a majority of its other signatories.
Tatiana Valovaya, director-general of the UN in Geneva, said it had carved out a reputation as a place where "discussions can take place in the greatest confidence and neutrality".
On Friday, Libya's warring rival administrations signed a permanent and immediate ceasefire agreement at the Palais des Nations, following years of turmoil and bloodshed.
And an international treaty banning nuclear weapons is on the verge of coming into force, on Friday becoming just one ratification short of the 50 required.