Cpl. Frederick of the Wayne County Airport Police and his bomb-sniffing dog Spencer patrol at the Detroit Metropolitan Airport on Saturday in Romulus, Michigan. Airports and airlines across the US moved rapidly to tighten security after a man tried to set off explosives on a plane flying from Amsterdam to Detroit. Photo: AFP

The father of a Nigerian man charged with trying to blow up a transatlantic jet on Christmas Day had voiced concerns to US officials about his son.
US investigators on Sunday tried to piece together terrorism connections of a Nigerian man who has been charged with attempting to blow up a US jetliner after reportedly confessing that he had been trained by al-Qaeda in Yemen.
Airport security was stepped up worldwide after the botched terror attack as British police raided premises where the suspect, the son of a wealthy Nigerian businessman, was thought to have lived while studying at a London university.
The father, a top Nigerian banker, warned US authorities last month about 23-year-old Umar Farouk Abdulmutallab's extreme views, say officials.
US sources confirm a file was opened, but say the information did not warrant placing the accused on a "no-fly" list.
Abdulmutallab was formally charged by a US federal judge at a Michigan hospital where he is being treated for burns after allegedly trying to detonate a device.
'Sewn in underpants'
The detainee reportedly smiled as agents brought him in to the room in a wheelchair, dressed in a green hospital robe and with a blanket over his lap.
High explosives are believed to have been moulded to his body and sewn in to his underpants.
He was immediately overpowered by passengers and crew aboard Northwest Airlines Flight 253, minutes before it was due to land in Detroit from the Dutch capital Amsterdam.