WASHINGTON— The mail bomb found inside a cargo plane north of London could have exploded, British Home Secretary Theresa May said Saturday after investigators completed a preliminary investigation.May said the plane carrying the package from Yemen may have been the target, and if the bomb had detonated, the explosion could have brought down the aircraft.RELATED:Obama: 'Terrorist threat' on Jewish targets thwartedUS Jewish groups told to be on high alert after terror plot"But we do not believe that the perpetrators of the attack would have known the location of the device when they planned for it to explode," May said. "At this stage we have no information to indicate another terrorist attack is imminent."US investigators have said the mail bombs found in the United Arab Emirates and England on Friday were headed to two synagogues in Chicago.Yemeni authorities are checking dozens more packages in the search for the terrorists who sent the bombs.Authorities on three continents thwarted the attacks Friday when they seized explosives on cargo planes in the United Arab Emirates and England. The plot sent tremors throughout the US, where after a frenzied day searching planes and parcel trucks for other explosives, officials temporarily banned all new cargo from Yemen. Several US officials said they were increasingly confident that al-Qaida's Yemen branch, the group behind the failed Detroit airliner bombing last Christmas, was responsible.President Barack Obama called the coordinated attacks a "credible terrorist threat." The bombs were discovered just days before the US national elections.A Yemeni security official said investigators there were examining 24 other suspect packages in the capital, San'a. He spoke on condition of anonymity because he was not authorized to release information and refused to provide more details.Authorities were questioning cargo workers at the airport as well as employees of the local shipping companies contracted to work with FedEx and UPS, the official said.In Dubai, where one of the two bombs was found in a FedEx shipment from Yemen, police said it contained a powerful explosive and bore the hallmarks of al-Qaida.The white powder explosives were discovered in the ink cartridge of a computer printer, said a police statement carried by the official state news agency WAM. The device was rigged to an electric circuit, and a mobile phone chip was hidden inside the printer, the statement said.The police said the bomb was prepared in a "professional manner."Yemen promised to investigate the plot. The US has FBI, military and intelligence officers stationed in the country to conduct an inquiry. There are only a handful of international shipping locations in the impoverished Arab nation, but US officials worried that record keeping would be sparse and investigators would have to rely more on intelligence sources to identify the would-be bombers. The other package was found at an airport in central England. Preliminary tests indicated both packages contained PETN, a powerful industrial explosive and the same chemical used in the attempted Christmas attack, US officials said.