US intelligence agencies have thwarted a plot to blow up a plane as it entered the US using an improved version of the "underpants" bomb that failed to detonate on Christmas Day 2009. The FBI confirmed yesterday that it was conducting tests on a seized explosive device similar to others used by an al-Qa'ida offshoot in Yemen. Associated Press reported US officials saying a would-be suicide bomber was given the device last month by the Yemen-based organization. But the bomber, apparently not given specific instructions, had yet to pick a target or buy an airline ticket at the time of his arrest. White House spokeswoman Caitlin Hayden said US President Barack Obama was advised of the bomb plot last month and was assured the device posed no threat to public safety. The White House played down suggestions that the plan to destroy a passenger jet entering the US was timed to coincide with the anniversary last week of the killing of al-Qa'ida leader Osama bin Laden. Asked about possible terrorist activity on April 26, White House spokesman Jay Carney said the US had no credible information that groups, including al-Qa'ida, were plotting attacks linked to the death of bin Laden. The US Homeland Security Department was emphatic as well: "We have no indication of any specific, credible threats or plots against the US tied to the one-year anniversary of bin Laden's death." Associated Press learned of the alleged plot last week but complied with a request from the CIA and the White House to delay breaking the story while related intelligence operations continued.