Former Luxembourg Prime Minister Jean-Claude Juncker, the EU's longest-serving elder statesman, has thrown his hat into the ring for the presidency of the European Commission to succeed Jose Manuel Barroso.

Mr Juncker, 59, governed for 19 years until a general election defeat last October and also chaired euro zone finance ministers for eight years from 2005 to 2013.

He told Germany's Inforadio: "I would be willing (to do the job), in principle, if the election programme and other things work out."

Voters across the 28-nation European Union vote in late May to elect a new European Parliament.

Then in June, EU leaders nominate a candidate to head the executive European Commission, taking account of the election results.

The new legislature must then vote to confirm the nominee by an absolute majority of the 751 lawmakers.

Mr Juncker, a convinced European federalist and member of the centre-right Christian Social party, was asked whether he would run to be the lead candidate of the European People's Party, the main conservative grouping in the EU legislature, with a view to the Commission presidency.

European Parliament leaders have contended that the lead candidate of the party that comes first in the election should be nominated as Commission president.

However some EU leaders, notably German Chancellor Angela Merkel, have voiced reservations about that procedure, which they see as a parliamentary power-grab, stretching the terms of the 2009 Lisbon Treaty.

Mr Barroso, a conservative former Portuguese prime minister, has run the Commission since 2004.

The Socialist group, the second largest force in the current legislature, has nominated Martin Schulz, a German Social Democrat who now presides over the European Parliament, as its candidate.

Other possible contenders for the EPP nomination include French conservative Michel Barnier, who is the European commissioner for the internal market and financial regulation.

However, political sources have said Ms Merkel may prefer a serving conservative prime minister such as Poland's Donald Tusk, Finland's Jyrki Katainen or possibly Taoiseach Enda Kenny as Commission president.

The EPP will anoint its candidate at a convention in Dublin on 6-7 March.

The third largest political group, the centre-right Liberals, is holding a primary contest between former Belgian Prime Minister Guy Verhofstadt and Finnish European Commission Vice-President for Economic and Monetary Affairs Olli Rehn.