Brussels lowered European flags to half mast in order to give tribute to Kohl.
Kohl served as chancellor of West Germany from 1982 to 1990, and then of reunified Germany from 1990 to 1998.
Former U.S. president George Bush Senior once described him as the most important European leader of the late 20th century.
In a 2012 tribute, former USA president Bill Clinton described Mr Kohl as one of post-war Europe's defining statesmen. "A truly great German has died", said Gabriel in a statement.
Kohl took power in 1982, leading West Germany into a new era which would result in the reunification of East and West Germany.
"Mournful news has come that former German Chancellor Helmut Kohl passed away, the man who had done much for promoting equal relations between his country and a new democratic Russian Federation", she said.
Kohl was helped in securing German unity by his friendships with French President Francois Mitterrand and Soviet leader Mikhail Gorbachev, who approved North Atlantic Treaty Organisation membership for a united Germany and agreed to pull Soviet troops out of East Germany.
He praised former British Prime Minister Margaret Thatcher for her honesty, even as he recalled a confrontation with her just days after the fall of the Berlin Wall.
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"I thought it was freaky really, it was like we had elbowed the player the way it was going on", said Hudson. We don't want to be fearful or negative or sit back and allow Mexico to do what they want.
EU Council President Donald Tusk "Helmut's death hurts me deeply".
The following year, Kohl plunged his party into crisis when he admitted accepting undeclared donations during his time as chancellor.
The Former Chancellor of the Federal Republic of Germany Helmut Josef Michael Kohl was born on April 3, 1930 in Ludwigshafen am Rhein, Germany.
Juncker recalled that only three people have been bestowed Honorary Citizenship of Europe Jean Monnet, Jacques Delors and Helmut Kohl. Together with his French ally President Francois Mitterrand, he was responsible for the introduction of the Euro.
Prime Minister Theresa May said Mr Kohl was a "giant" of European history.
Former protegee Angela Merkel lauded Kohl's contribution to German and European integration in 2012, on the 30th anniversary of his becoming chancellor, declaring that Europeans were "united in our luck" thanks to Kohl's efforts.
"My mentor, my friend, the very essence of Europe, he will be greatly, greatly missed".
"As the first chancellor of a unified Germany since 1945 he was a giant of European history".
Martin Schulz, the Social Democratic Party's challenger to Chancellor Angela Merkel in Germany's September election, says despite their political differences, former Chancellor Helmut Kohl deserves "respect and recognition" for his accomplishments.
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