BERLIN (Reuters, AFP) - German state-owned railway operator Deutsche Bahn will take legal action against a train drivers' union staging a four-day strike from Thursday to Monday which has paralysed passenger and freight transport across the country, the company said.

Politicians and industry groups have voiced fears about the impact of the strike, which is the longest in Deutsche Bahn's 20-year history, and will hit weekend celebrations for the 25th anniversary of the fall of the Berlin Wall.

Deutsche Bahn said it had decided reluctantly to take out an injunction in a Frankfurt labour court after the GDL drivers'union, which has about 20,000 members, rejected its offer of mediation talks.

The work stoppage by the GDL train drivers' union hit long-distance and regional rail services as well as commuter S-Bahn train networks from 0100 GMT (9am Singapore time) as planned.

The strike - the union's sixth bout of industrial action since September - kicked off with freight services on Wednesday, added passenger trains on Thursday and is due to continue until early Monday.

Deutsche Bahn said the walkout had caused "massive disturbances" but that it aimed to ensure a third of intercity transport services kept running.

About 30 percent of regional trains and S-Bahn services were running in the west and north of the country, about 40 percent in the south and between 15 and 30 percent in the east, it said.

Chancellor Angela Merkel has insisted that the right to strike has to be carried out "responsibly" and "with a sense of proportion."

Late Wednesday, the GDL union rejected an arbitration offer by Deutsche Bahn, which has slammed the latest walkout as "pure bullying".

GDL says Deutsche Bahn is stonewalling in talks over workers' demands for a five-percent wage hike and a shorter working week of 37 hours.

Union leaders also want to represent other groups of employees within Deutsche Bahn such as conductors, catering staff, dispatchers, and not just drivers.