Pfizer's $160bn dollar merger deal with Dublin-based Allergan was terminated by its board overnight.

Measures introduced by the US Treasury Department – the third in fifteen months – are believed to have directly targeted this deal in that it disallowed the strong acquisitive growth made by Allergan over the past three years to meet the scale threshold required for this deal.

The latest Treasury moves impose a three-year limit on overseas companies bulking up on US assets to avoid ownership limits for a subsequent inversion deal, meaning that Allergan’s key deals over the past 36 months cannot be counted.

This is unlikely to impact on the more than 4,000 employees of both groups in Ireland

US President Barrack Obama highlighted the importance of curbing these deals:

"When companies exploit loopholes like this... it sticks the rest of us with the tab and it makes hard-working Americans feel like the deck is stacked against them," he told a press conference in Washington.

He added that wealthy companies and individuals cannot be allowed to "game the system."

Mr Obama has previously criticised US firms who magically become Irish overnight.

Other Irish-related inversion deals in process include Johnson Contols/Tyco ($16bn) and Shire/Baxalta ($32bn).