Birthday tributes display Merkel's power

During a press conference after the EU summit, a German journalist sang an awkward "Happy Birthday, dear Bundeskanzlerin" to which she replied: "Maybe I should have sung along, it would have sounded better. But thank you."

Germany's largest-selling tabloid, Bild, recorded a version of an old folk song - "We love the storms" - sung by several politicians and pop stars in her honour and published Merkel portraits drawn by readers.

Later on, in Berlin, she invited some 1,000 guests to a history lecture rather than a glamorous party to mark her birthday.

With unmatched popularity rates and the status of the longest-serving and most powerful of EU leaders, Merkel has achieved remarkable success after starting out as a scientist in the then East Germany.

A Forsa poll on Wednesday showed that after more than eight years in power, 59 percent of Germans would vote for her rather than for her Social-Democrat rival and vice-chancellor, Sigmar Gabriel (14 percent).

An Infratest dimap poll earlier this month said 71 percent of Germans were happy or very happy with her work.

Meanwhile, speculation she might step down before the end of her current term to take up an international top post - the presidency of the EU council or the United Nations - re-emerged earlier this month.

Der Spiegel magasine quoted unnamed sources in her entourage saying she would rather step down while popular than to be forced out of office like her mentors and predecessors, Helmut Kohl and Konrad Adenauer.

Her spokesman denied it and said she plans to see out her term, which ends in 2017.

For his part, Kohl - the architect of German reunification, who in 1999 had to step down in a party funding scandal which saw Merkel distance herself from him - urged her to remain committed to the European project.

In an open letter published also in Bild, the 84-year old Kohl said it is thanks to German reunification that Merkel had "completely new chances in a free Germany which you used and which brought you to the helm of our country".

He urged Merkel to "stick to a united Europe, continue political unification, and stand for the stability" in Europe and the eurozone.