BRUSSELS (AFP) - The European Union flew flags at half mast and observed a minute's silence on Thursday to honour the 12 people killed in the militant attack on the Charlie Hebdo satirical magazine in Paris.

European Parliament lawmakers and staff gathered outside the building in the rain in Brussels at 10.45am to "show their solidarity" with France, president Martin Schulz said.

Separately, European Commissioners observed a minute's silence with the Latvian government at a meeting in Riga to mark the start of Latvia's six-month presidency of the European Union.

The European Commission, the executive arm of the 28-nation EU, also said all activity at its offices in central Brussels would also come to a halt at midday as a mark of respect.

Mr Donald Tusk, the president of the European Council, which groups the leaders of the EU's 28 member states, said he too had invited staff to also hold a minute of silence.

Meanwhile, the blue EU flag with yellow stars is also being flown at half-mast on EU buildings to mark the killings.

The attack has stoked fears of other attacks as militant fighters return radicalised to Europe from the bloody conflicts in Syria and Iraq.

In France, the police are seeking two brothers in connection with Wednesday's attack, one of them Cherif Kouachi, being a militant who has been well-known to anti-terror police for many years.

Cherif was jailed in 2008 for his role in sending fighters to Iraq.