The bank said it "assumed" there would be economic red lines, like oil at $100 a barrel, that the US would be unwilling the cross.

Since taking control in 1965, Buffett grew a struggling textile mill into a global conglomerate.

O'Leary described his choice of language as "careless" and said "it won't happen again".

The failure led to more than 2,000 flights being cancelled and hundreds of thousands of passengers affected.