LONDON - British postal workers began a two-day strike Thursday in a bitter row over pay, conditions and modernisation, causing widespread disruption to mail services.

Up to 120,000 staff were expected to walk out during the strike called by the Communication Workers Union (CWU), after hopes of a last-minute deal with state-owned postal operator Royal Mail collapsed on Wednesday.

Royal Mail managers insisted they were still open to talks, while Business Secretary Peter Mandelson urged union leaders not to politicise the dispute.

"I don't think trading insults in this situation helps resolve the dispute.

Politicising or dramatising it is useless. People need to focus on what issues are dividing them," Mandelson said.

On Thursday, some 42,000 mail centre staff and drivers were on strike, while 78,000 frontline delivery and collection postmen are due to join them on Friday.

Union leaders blame the government and Royal Mail for trying to scupper an agreement. They have also warned that the walkout, the first national strike by postal workers since 2007, may not be the last.

Royal Mail has branded the action "wholly unjustified", warning it would drive customers away from the business at a time when it faces growing competition from the private sector as well as fewer people sending letters.

Prime Minister Gordon Brown agreed, saying: "This strike will be self defeating if all it means is that less people use the Royal Mail."

He added: "It's essential that everybody gets round the table... as soon as possible."

Royal Mail has said it will recruit up to 30,000 temporary staff to cope with the strike and the Christmas holiday rush.