The postal workers marched to the Belfast rally

Communications Workers Union spokesman Owen Davey said after an early morning meeting that the staff's position had not changed over the illegal action.

Post has been disrupted in the north, south and west of the city since the dispute began on 31 January. Deliveries in east Belfast have continued.

It is also believed that some mail to the north west has not been delivered

On Wednesday, Charlie Kelly of the CWU in Londonderry said his members would not join an unofficial dispute.

"They are expecting the Derry staff to go out and under no circumstances will they as long as the strike is unofficial," he said.

ROYAL MAIL'S ADVICE No mail in north, south and west Belfast - deliveries in east of the city unaffected No more special delivery items accepted across NI No mail posted in Belfast being processed Items posted in NI for delivery to Britain, Irish Republic and internationally not being dispatched Most incoming British and international mail should be delivered People expecting urgent mail should contact that organisation and explore alternatives such as telephone or email

Royal Mail and the Social Security Agency have issued more advice to customers affected by the dispute.

The agency said people who normally received benefit payments through the mail should collect it from their nearest Post Office from Friday.

Royal Mail has cancelled special delivery services and warned that packages to Britain would not be delivered.

It said items posted in the province for delivery to Britain, the Irish Republic and internationally were not being dispatched

However, most mail coming into Northern Ireland will be dispatched, with the exception of strike areas.

Earlier, official watchdog Postwatch said Royal Mail had not done enough to inform the public.

Staff at the delivery office in Tomb Street walked out last week in a dispute about disciplinary procedures. Mail posted in Belfast is not being processed or delivered.

On Wednesday, Mr Davey said: "Again we repudiated the action and asked them to go back to work, pointing out that the action was illegal.

"They were adamant that their resolve was strong and they were staying out until the Royal Mail concedes to what is a reasonable request for an independent employee and industrial relations review."

Royal Mail said it met representatives from unions and the Labour Relations Agency on Tuesday.

The strike action began on Tuesday last week

The Irish Congress of Trade Unions has offered to mediate in the dispute.

The unofficial action was started by more than 200 postal workers at the city's Tomb Street depot.

It was blamed on difficulties between staff and management over disciplinary procedures and other issues in the north Belfast section.

Royal Mail has said workers need to come off the picket line before they will enter into negotiations with them.

However, staff involved in the dispute have said they have no intention of returning to work until the original dispute in Belfast has been resolved.