The severe economic fallout from the attacks on the US is likely to hit the tourism sector particularly hard, according to Bord Fáilte.
Ireland's tourism industry is already reeling from a £200 million bodyblow as a result of the foot-and-mouth crisis.
Last year, over a million North American tourists - out of 6.2 million visitors - spent £557 million in Ireland.
In any one day this month there would normally be 35,000-45,000 US tourists in the country and, prior to the attacks, a further 200,000 had been expected to visit before the end of the year.
"How badly numbers will be hit is anybody's guess just now, but it is a gloomy picture. When there is conflict the Americans don't tend to travel out of their own country, and the psychological impact remains for a long time," a Bord Fáilte spokesman said.
Historically, the figures show it takes on average three years for the US tourist market to recover to previous levels when it suffers the impact of a terror attack or a war.
There are also expected to be grim consequences in the technology sectors.
Mr Ahern recently expressed "great concern" about a spate of Information and Communications Technology (ICT) job losses since July. "However, I want to emphasise that Ireland is well-positioned to weather this storm," he said.
The Industrial Development Authority (IDA) said it is too early to assess the impact of the attacks. "Every single country in the developed world is suffering from job losses but statistically we are doing relatively well," an IDA spokesman said.
The country's 300 ICT companies employ over 50,000 directly and account for a quarter of total exports. Ireland is the biggest exporter of computer software in the world, and many more are employed in supply companies for the sector.
AFP