Sinn Féin has denied allegations made by a DUP MP in the House of Commons that Mid Ulster Assembly member Francie Molloy was a police informer.
The allegation, by Upper Bann MP David Simpson, was made under parliamentary privilege and Mr Molloy challenged him to repeat his claim in public outside Westminster.
Deputy First Minister Martin McGuinness called for Mr Simpson's remarks to be treated with contempt. "Francie is a well-respected republican and these unfounded allegations will not affect in anyway the esteem in which he is held.
"These cowardly allegations, made behind the cloak of privilege, are deeply irresponsible."
Mr Molloy said that since Mr Simpson had first "briefed sections of the media" about his alleged role as a police informer, he had been "inundated with messages of support from republicans across Ireland who know me and know my record of service to the republican cause".
He accused Mr Simpson of being the latest in a long line of unionist MPs "who have in the past abused parliamentary privilege to chase headlines regardless of the consequences".
"Given this history I would expect all of us, the media included, to approach this latest stunt with extreme caution." He added: "Unionist death squads in the past never stopped me going about my work representing Sinn Féin and the people who elect me. A unionist MP standing up in the British House of Commons will not succeed in this either."