British postal workers said Wednesday they will launch a second round of national strikes this week after talks to end a bitter dispute over pay, working conditions and modernisation broke down.

The Communication Workers' Union (CWU) said the three-day strike would begin at 4:00am (GMT) Thursday, one week after a two-day walkout caused major disruption for the state-owned postal service Royal Mail.

Royal Mail condemned the fresh action and accused trade union leaders of walking away from the negotiations.

The strikes come as Royal Mail is already losing business, with fewer people sending letters and growing competition from the private sector.

CWU deputy general secretary Dave Ward said fresh talks this week were "the most useful and productive" since the long-running dispute began but failed to result in an interim deal that would allow them to call off the strike.

- At this point of time, we have not had confirmation as to whether our proposal is acceptable and therefore the strikes previously announced for the next few days will take place - he said.

Royal Mail managing director Mark Higson also said that "huge progress" had been made this week but said the CWU leadership had failed to agree.

- The central issue remains the CWU's opposition to Royal Mail's essential modernisation plans, without which the company simply does not have a future - he said in a statement, adding that they were still open for talks.

About 43,700 mail centre staff and drivers across Britain will walk out on Thursday, followed by 400 mail centre assistants on Friday and 77,000 delivery and collection staff on Saturday.