The Irish group, who come from Sligo and Dublin, helped launch the appeal in London on Sunday.

But Matt Carthy, national organiser of Sinn Fein Youth, called their backing "insensitive in the extreme", given the history of the British Army's involvement in Ireland.

RCA Records issued a statement saying it was the company's decision to involve Westlife in the appeal, not the group's.

"RCA Records, on behalf of Westlife, would like to make it clear that the decision to involve Westlife in the poppy appeal was entirely that of the record company," it said.

The statement added the company was following "a tradition of involving high profile celebrities supporting charity organisations".

Sinn Fein says Westlive have insulted nationalists

Mr Carthy said what added insult to injury for the nationalist community was that the band had said they were honoured to take part in the poppy appeal.

There was nothing honourable about British army involvement in the past 30 years of conflict, he said.

"How can Westlife justify their decision to those relatives whose loved ones have been killed by the British army?

"What do they have to say to the parents of Karen Reilly who saw Lee Clegg walk free after being convicted of killing their daughter?" he asked.

Mr Carthy, a Monaghan district councillor, said the party was calling on the group to withdraw their support for the event.

"At a time when all concerned are working to heal the scars of decades of conflict, Westlife's decision is insensitive in the extreme," he said.

'Outdated protest'

But Ulster Unionists accused Sinn Fein of engaging in a "silly out-dated protest."

Jeffrey Donaldson, MP, said it was sad Sinn Fein was attacking the group for helping the poppy day appeal.

"Sinn Fein are constantly harping on about how they are victims, but they constantly insult the memory of the thousands of people who died in two world wars - many of them Irishmen - by making this kind of silly out-dated protest.

"It really is time they entered the real world," he said.