This was an opportunity for Mr Adams to offer some explanation about why two IRA explosives experts and a Sinn Fein political officer were arrested

Congressman Henry Hyde

He said he was declining the invitation to attend on Wednesday because his priorities were to "defend the peace process, to defend Sinn Fein's essential contribution to it.

"And to give proper consideration to the plight of the three men presently in detention in Colombia, their right to a fair trial".

Mr Adams said the men's lawyers said the hearings and his presence at them could "well be prejudicial to any possibility of a fair trial".

He sent his answer to chairman of the US House of Representatives International Relations Committee, Congressman Henry Hyde.

In a strongly-worded statement, Mr Hyde said the committee's invitation had been "an opportunity for Mr Adams to offer some explanation about why two IRA explosives experts and a Sinn Fein political officer stationed in Cuba were arrested last August following a visit to a safe haven controlled by the Revolutionary Armed Forces of Colombia, FARC, a designated terrorist organisation."

Congressman Hyde added: "FARC and other narco terrorist groups in Colombia are responsible for 90% of the cocaine and 70% of the heroin sold on America's streets.

"Terrorism imperils Colombian democracy, and the alleged IRA role in helping groups like the FARC to perpetuate this violence poses a direct threat to US national interests."

Gerry Adams: "Danger of prejudicing trial"

After the arrest of Jim Monaghan, Martin McCauley and Niall Connolly in Colombia, Sinn Fein initially denied that Mr Connolly was its political representative in Cuba.

When it became apparent that this was untrue, the party said it had made a mistake.

Last month, Colombian prosecutors formally charged the three suspects - two from Republic of Ireland and one from Northern Ireland - with teaching bomb-making to Marxist rebels, bringing the men's trial a significant step closer.

The three men have denied links with the IRA or Colombian guerrillas.

They have said they have been "framed as part of attempts to damage peace talks between the government and rebels".

On Tuesday Mr Adams said he was satisfied with an IRA statement last September when it said it "sent no-one to Colombia to train or to engage in any military operation with any group".

The West Belfast MP said the hearings were "only coincidentally about Ireland" but "essentially about the relationship between the USA and Colombia".

'Affront'

But reacting to his announcement, Ulster Unionist assembly member James Leslie said it was "an affront to the biggest democracy in the world".

SDLP's Alex Attwood: "What has Sinn Fein got to hide?"

Mr Leslie added: "Adams may not be prepared to stand up and be counted in the USA but he will not be able to evade scrutiny here."

Ulster Unionist leader David Trimble had called on Mr Adams to testify at the US hearings.

Chairman of the nationalist SDLP Alex Attwood said Mr Adams' refusal to attend the committee hearing "will raise questions as to what Sinn Fein has to hide".

"Sinn Fein call for accountability of others for their actions but appear to wish to avoid accountability for their actions," he added.

At the weekend, a leading American official said the US hearing into IRA links with left-wing FARC paramilitaries would not prejudice the trial of three republicans in Colombia because it was not a jury trial.

Mr Mackey, an official with the House Committee on International Relations at Capitol Hill, added: "This hearing is not about the Irish peace process - it is about US national interests in our backyard."