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Sinn Fein is on high alert amidst ramped-up death threats against chief negotiator Martin McGuinness, the Deputy First Minister of Northern Ireland.

Sinn Fein sources say the death threats are higher than anything else in the past. "This is a very worrying development," a source said. "There is no question that these threats are being taken very seriously.

"We have attempted to reach out to some of these dissidents but our efforts have not been returned."

Irishcentral understands that McGuinness is particularly vulnerable to death threats as he does not accept full State security.

Meanwhile, a defiant McGuinness told a press conference in Derry today that those who made the threats against him are "imposters."

He said that he had a job to do - and that he intended to do it. He also revealed that his wife and children had been verbally abused by "mouthpieces" on the street.

"People are trying to hijack the Republican cause for their own purpose. Well they're not going to succeed. We have a job to do. Yes it is a difficult job, and yes it may be a dangerous job, and yes some of us my lose our lives in the future.

"But I am not going to be threatened, I am not going to be intimidated and I am certainly not going to live my life in fear."

In an statement released earlier today McGuinness said that the death threats would not stop him from continuing to build Northern Ireland’s peace process.

"I have spent my entire adult life engaged in the republican struggle to bring about Irish unity and independence,” he said.

 “One thing is for certain: neither I nor Sinn Féin has allowed these sorts of threats to stop us representing our community and driving forward the republican agenda in the past and we will not allow it to deflect us from our work in the future.”

He added that this would not be the first time opponents had sought to silence him.

 “These have come from a variety of British state agencies and their surrogates in the loyalist gangs. It now seems that some of these small groups have now taken their place in that company”

He said the perpetrators had "betrayed the desires and political aspirations of all the people who live on this island and they don't deserve to be supported by anyone."

This comes at a time at an upsurge of activity from dissident Republican groups, who killed two British soldiers – the first soldiers to have been killed in Northern Ireland in over a decade – and a Catholic police officer last month.

McGuinness had described the dissidents as "traitors" after the murders.

At a public meeting in County Tyrone earlier this week, Sinn Fein President Gerry Adams strongly attacked the dissidents, saying that "Militarism, elitism or adventurism is no substitute to strategy, for tactics, for common sense."

He said Republicans could secure a united Ireland through policy. 

"Some take exception to remarks by republican leaders and seize on these in an entirely self-serving and negative way," he said.

"Others threaten to kill us, or they actually attack our homes or offices."

"Let me make it clear that Sinn Fein is not going to roll over and surrender our struggle to any of these elements."