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Here's reaction from other leaders around the world:
“The British people have decided to leave the European Union. As it defines the next chapter in its relationship with the EU, I know that the United Kingdom's position in NATO will remain unchanged. The UK will remain a strong and committed NATO Ally, and will continue to play its leading role in our Alliance.”
"I profoundly regret this decision for the United Kingdom and for Europe, but the choice is theirs and we have to respect it,” French President Francois Hollande told reporters today after a meeting with his ministers.
French leftist Jean-Luc Mélenchon said on French radio this morning, “This is the end of a world that begins with this Brexit. This teaches a lesson to the whole of Europe; either we change it or we leave it. This is the time for a plan B.”
Prime Minister Enda Kenny said the result has "very significant implications" for Ireland. He was due to make a statement after a special meeting of ministers today.
Spain's foreign minister proposed sharing Britain's small Mediterranean enclave of Gibraltar after Britain voted to exit the European Union, saying it would allow the overseas territory to maintain access to the E.U.'s single market.
After an emergency meeting with parliamentary heads, German Chancellor Angela Merkel expressed "great regret" over the result and warned Europe shouldn't draw "quick and simple conclusions" that would create further division.
Norbert Röttgen, a senior member of Angela Merkel's Christian Democratic Union (CDU) Party, decried Brexit as the "biggest catastrophe in the history of European integration."
Foreign minister Paolo Gentiloni said, "The decision of the British voters must be a wake-up call."
Konstantin Kosachev, head of the foreign affairs committee in Russia's upper house of Parliament, told the Interfax news agency that the E.U. "has not solved its main problem: to become understood by and convenient for the broader masses of the population."
But “this is an issue for the E.U. foremost to draw conclusions from, and Britain only second," he said.
The Foreign Minister of Japan, Fumio Kishida, released a statement this morning that the country will closely observe the impact of those developments on Japan and the international community. Kishida added that the government of Japan will continue to make efforts to maintain and strengthen the Japan-U.K .relations.
South Korea's economic and financial authorities have held an emergency meeting to discuss ways to fend off any possible fallout from the British withdrawal from the European Union, the news agency Yonhap reported.
Prime Minister Alexi Tsipras said the result is a "negative development,” adding that the migrant crisis was partly to blame for the Brexit vote.
Swedish prime minister Stefan Löfven said the vote result was a "wake-up call" for the E.U., and says it must show it can respond to people's expectations.