Former German chancellor Helmut Kohl, who was celebrated as the father of German reunification in 1990 and an architect of European integration, has died at the age of 87, according to German media.

Germany's longest serving post-war leader died in his house in Ludwigshafen, in the western state of Rhineland-Palatinate, said the Bild daily newspaper, whose management had close ties with the conservative politician.

Mr Kohl was chancellor from 1982 to 1998.

European Commission chief Jean-Claude Juncker paid tribute to Mr Kohl, describing him as the "very essence of Europe."

"Helmut's death hurts me deeply. My mentor, my friend, the very essence of Europe, he will be greatly, greatly missed," the former Luxembourg premier said on Twitter.

President Michael D Higgins paid tribute to Mr Kohl this afternoon.

"He will be remembered for his 16-year tenure as Chancellor, as well as for his role in the reunification of East and West Germany in 1990."

"His deep commitment to the European project was unshakable, referring as he often did to the common European House, in the construction of which everyone would have a role.

"On behalf of the people of Ireland I wish to convey our deepest sympathies to his family and to the people of Germany," said Mr Higgins.

A spokesman for German Chancellor Angela Merkel voiced deep sorrow that "great European" Mr Kohl has died.

Former US president George HW Bush described him as "a true friend of freedom" and "one of the greatest leaders in post-War Europe".

"Helmut hated war - but he detested totalitarianism even more," the former president said in a statement.

"Working closely with my very good friend to help achieve a peaceful end to the Cold War and the unification of Germany within NATO will remain one of the great joys of my life."

Mr Kohl was a passionate advocate of European integration whose outlook was shaped by the two world wars that ravaged Europe and claimed the lives of his brother and uncle.

Together with French President Francois Mitterrand, the enigmatic socialist with whom he developed an unlikely personal bond, Mr Kohl helped steer a peaceful course for the continent during the twilight years of the Soviet Union, when the foundations of Europe's post-war order crumbled and had to be reset.

By committing to anchor Germany within Europe under a common currency, he overcame resistance to reunification from Mr Mitterrand, Soviet leader Mikhail Gorbachev and Margaret Thatcher, the British prime minister who feared the return of a powerful, united Germany.

For all his accomplishments as chancellor, Mr Kohl's life was tinged by controversy and personal tragedy after he left office in 1998 as Germany's longest-serving leader since Bismarck.

In 2000, he was forced to resign as honorary chairman of the Christian Democratic Union (CDU), the party he had led for 25 years, after admitting to receiving close to €1m in illegal cash donations during his time as chancellor, which he doled out to local party organisations at his whim.

He refused to reveal where the money had come from, saying he had given the donors his "Ehrenwort", or word of honour, not to disclose their names. The scandal made him a virtual pariah in his own party for years.

Ms Merkel, the shy physicist from communist East Germany whom Mr Kohl had plucked from obscurity to join his cabinet after the November 1989 fall of the Berlin Wall, turned on him at a crucial moment during the scandal, ensuring his exile. Ties between the two had been frosty ever since.

Former Taoiseach pays tribute

Former Taoiseach John Bruton released a statement saying he was very sad to learn of the death of Mr Kohl.

In the statement, Mr Bruton said:  "Along with President Gorbachev, he was the most important constructive European leader of the past century.

"Underestimated initially, he was a man with a deep sense of history.

"I remember him describe movingly how close relatives of his had died in both the First and Second World Wars, and said that that was one of the reasons why he was absolutely determined that war should never happen again in Europe.

"He understood that the pre war system of relations between states in Europe had to be fundamentally changed, if peace was to be guaranteed.

"While he was the man who achieved a united Germany, he wanted to ensure that a united Germany would be one that would be in total harmony with its neighbours.

"He saw the European Union, and the euro, as new arrangements that would tie the interests of his native Germany so closely with all its neighbours, that conflict between them would be unthinkable ever again.

"He was prepared to sacrifice the independent Deutschsmark to build a European structure of peace. He understood that there are some causes that transcend economics

"He came to Ireland on a state visit at my invitation when I was Taoiseach and I met him numerous times while he was Chancellor, and afterwards at EPP meetings during the Convention on the Future of Europe.

"He was an inspiring figure, who could be frank to the point of bluntness, if he felt that was what was needed to achieve his goal of profound unity among Europeans."