US urges vigilance after underwear bomb plot foiled

A plot by al-Qaeda in Yemen to detonate an upgraded version of the failed 2009 "underwear bomb" has been disrupted, US officials say.

The device was seized by intelligence operatives and is in US custody undergoing technical and forensic analysis, the FBI has said.

Reports said no target had been chosen and no plane tickets purchased by the time the alleged plot was foiled.

US Defence Secretary Leon Panetta said security services must remain vigilant and would "do everything necessary to keep America safe".