The leader of the opposition centre-right Christian Social Union in Germany, Theo Waigel, says the party will go to the Constitutional Court to challenge government plans to liberalise the country's laws on citizenship.

Mr Waigel -- a former finance minister -- was speaking before the opening of the annual congress of the party, which is the Bavarian ally of the main opposition Christian Democrats .

He said all democratic means would be used to challenge the plans, which would abandon the principle of nationality by blood and make it easier for foreigners -- especially those born in Germany -- to obtain German citizenship and hold dual nationality.

Shortly before Mr Waigel's statement, the Interior Minister, Otto Schily, strongly attacked the two centre-right parties, saying they were out of touch with reality.

The two parties have already announced plans for a massive petition against the laws -- a move criticised by the governing Social Democrats, immigrant groups and Jewish organisations.