Theresa May has promised a review of air freight security following the discovery of two bombs on planes in the UK and Dubai.
The Home Secretary said: "Certainly, we have to look at our processes of searching and how we detect these devices."
The terrorists behind the cargo bomb plot would not have known exactly where the deadly device was to strike, she added.
The unpredictable routes taken by freight planes meant it was "difficult" to say even now whether the explosions would have happened over Britain or America.
The comments came with the hunt for the al Qaida linked masterminds in full swing.
A woman medical student arrested by authorities in Yemen along with her mother on suspicion of posting the two bombs to synagogues in Chicago has reportedly claimed she was "tricked".
Prime Minister David Cameron said the explosive device found on a US-bound flight at East Midlands Airport was designed to blow a jet out of the sky - possibly over Britain.
The devices, hidden inside printer toner cartridges, are only thought to have been discovered en route at East Midlands Airport and in Dubai as a result of an intelligence tip-off.