By Jonathan Duffy BBC News Online correspondent in New York

Their cause has always been a united Ireland, but much of the cash that funds republican groups comes from the United States. So how will they fare amid the new crackdown on terrorism?

It took the attacks on 11 September to bring the full horror of terror attacks home to many Americans. And their sense of outrage is compounded by a feeling that this is a war on terror that cannot be won easily.

The attacks prompted a "war on terrorism"

Since then, the Bush administration has vowed to come down hard on terrorists operating in the US.

The president has enacted executive powers that allow for the freezing of all assets in the US of suspected Islamic terror groups.

While all American eyes are currently fixed on Muslim extremists, politicians in Northern Ireland have urged President Bush to extend the clampdown to those who raise funds for Irish paramilitary groups.

Without [US] funding, the IRA would not have nearly the same potential for violence

Jeffrey Donaldson Ulster Unionist MP

While Libya's donation of arms to the IRA in the 1980s has been the most public sign of where the republican movement has previously turned for support, the reality is that North America has been the most important link of all.

Following the emergence of the modern republican movement in 1969, the Provisional IRA quickly turned to its Irish-American supporters for funds and guns.

More than 30 years later, those support networks still exist, although the nature of the relationship has changed during the long road of the peace process.

Follow the money

Ulster Unionist MP Jeffrey Donaldson wants to see the strong measures extended to Noraid, which raises money for the republican party Sinn Fein, which itself has links with the Provisional IRA.

There's mutual regard between the Irish and the Americans

"Without their funding, the IRA would not have nearly the same potential for violence that it currently has," he says.

Noraid has openly expressed support for the IRA but says it gives money for humanitarian aid, and denies its donations are used for the purchase of arms.

Sinn Fein has, of course, come in from the cold in recent years. It was de-designated as a foreign terrorist organisation by the US State Department in 1994 after the start of peace efforts in Northern Ireland - a move which allowed its leader, Gerry Adams, to travel to the US.

Humanitarian aid

But other groups perhaps walk a finer line. John McDonagh, chairman of the New York-based Irish Freedom Committee, thinks he is in for a rough ride.

With all these new laws coming in, we could be banned

John McDonagh

His organisation's supporters are sympathetic to dissident republicans who oppose the move away from an "armed struggle" in Northern Ireland, although Mr McDonagh says its contributions only support the families of republican prisoners.

"With all these new laws coming in we don't know what is going to happen. It's possible that it could impact us. We could be banned," says Mr McDonagh, who is one of an estimated 40 million Irish-Americans.

While supporting what many would see as a terror group, he draws a line between the actions of the IRA and those of the 11 September attackers.

"There's no comparison. I don't think it's in the psyche of the Irish to become suicide bombers. The IRA gives warnings before its bombings. What happened here brings it to a whole new level."

Others would point to the fact that an attack by the dissident 'Real IRA' in Omagh in 1998 claimed the lives of 29 civilians, while hundreds of people were killed and thousands maimed in IRA bombings and shootings in more than thirty years of violence.

'Climate of hysteria'

But Mr McDonagh concedes that recent events could rub off on Irish republicans.

The Real IRA is blamed for the Omagh bombing

A legal challenge is being prepared against the ruling by Washington earlier this year to outlaw the so-called Real IRA and its political wing, the 32 County Sovereignty Committee.

Mr McDonagh believes these groups will not get a fair hearing in the "climate of hysteria in this country".

As for the immediate effect on fundraising, he can't comment.

"We've been having a break over summer, but we've got a sponsored five-mile fun run in October and a dinner and dance in January, so we'll wait and see if the take is down."

Colombian connection

But if support does start to flag, activists might want to look elsewhere for the reason, says Conor O'Clery, a New York-based journalist for the Irish Times.

Sinn Fein and the IRA's stock has been tumbling in Washington ever since Bill Clinton - a president who immersed himself in Northern Irish politics - left office, says Mr O'Clery, author of Greening the White House.

Bill Clinton made the peace process a priority

But the biggest knock came this summer when three suspected IRA men were arrested in Colombia, where they had allegedly been training Marxist guerrillas who are said to sponsor their war through drug running.

On top of this came a visit by Sinn Fein leader Gerry Adams to communist Cuba, one of the US's sworn enemies.

"The two words drugs and Marxism have done more damage to Sinn Fein than the attack on the World Trade Center," says Mr O'Clery.

"But you now have a climate of anti-terrorism which rubs off on a group connected with terrorism. It will tarnish them further."