British authorities are probing whether a package from Yemen containing explosives found on a cargo jet bound for the United States was a "viable" bomb, Home Secretary Theresa May said on Saturday.
US President Barack Obama said on Friday that the package found at East Midlands Airport in central England and another package discovered in Dubai both contained explosive material and were addressed to synagogues in Chicago.
"At this stage I can say that the device did contain explosive material. But it is not yet clear that it was a viable explosive device. The forensic work continues," May said.
Media reports said that the package was found inside a toner cartridge with wires attached to it.
Britain is "urgently considering" new security measures for air cargo from Yemen following the discovery of the package and is "in discussion with industry contacts" over the issue, May said.
The British government suspended direct flights from Yemen in January after a Nigerian "underwear bomber" with links to the Arab country allegedly tried to blow up a US airliner over Detroit on Christmas Day 2009.
The discovery of the two packages on cargo planes in transit for the United States sparked an international security alert. Other planes at US airports were checked because they were thought to contain items from Yemen.
Obama said at the White House on Friday that the packages were a "credible terrorist threat." He announced that they contained explosives before British authorities had given any confirmation.
British police said that a suspect package had arrived aboard an "American-registered cargo plane" at East Midlands Airport. The plane was en route to Chicago via Philadelphia.