Police in Northern Ireland investigating an abusive tweet targeting a senior unionist politician have contacted gardaí because they believe the person responsible is based in the Republic.

The tweet, from an anonymous account which has since been removed, mocked the death of the son of Northern Ireland's former economy minister Diane Dodds of the DUP.

RTÉ News understands that the PSNI cyber crime unit has identified the account holder and established that they live south of the border.

Detectives are believed to have contacted gardaí during the week to request assistance.

The abusive tweet was sent in response to a posting from Mrs Dodds wishing her followers a happy new year.

It mocked the death of Andrew Dodds, son of the former Stormont minister and her husband Nigel Dodds, a former MP and DUP deputy leader.

Their son was born with spina bifida and died in 1998 aged eight.

Two years earlier, five days before Christmas in December 1996, IRA gunmen attempted to murder Nigel Dodds while he and his wife visited their son in the children’s unit of Belfast’s Royal Victoria Hospital. He escaped injury but one of his police guards was shot in the foot.

PSNI officers interviewed Mrs Dodds about the tweet at her constituency office in Co Down on Tuesday.

Speaking today, she said the anonymous account had a history of abusive content.

"It’s designed to have a harmful, damaging impact on anyone that receives that and whoever sent that tweet knew the impact that it would have and that's why it was so particularly vile," she said.

"This account targeted me and it has a history of targeting those with whom it has a difference of political point of view, and that's designed to keep people quiet, to cower people, to bully people into being quiet.

"So, it targeted me in this instance, but I do know of other instances where it has targeted those people who are the innocent victims of Republican terrorism."

We need your consent to load this rte-player contentWe use rte-player to manage extra content that can set cookies on your device and collect data about your activity. Please review their details and accept them to load the content.Manage Preferences

Mrs Dodds said Twitter has a responsibility and duty to stop anonymous account holders using the platform to abuse people, and to co-operate with law enforcement agencies investigating such abuse.

"We live in a democracy and freedom of speech is a precious part of our democracy. But what freedom of speech comes responsibility," she said.

"Twitter has a responsibility to ensure that people are not harmed, harassed by this kind of malicious communication so I hope that wherever the investigation takes the PSNI that they will get the support of the authorities in whatever area it is, or whatever country it is, or whatever part of Ireland it is, to go after those people and bring them to justice."

Earlier this week, Twitter said in a statement that it wanted to "reiterate our commitment to ensuring that Twitter doesn't become a forum that facilitates abuse".