LONDON - A SUSPECT package from Yemen found on a US-bound cargo plane at a British airport was 'viable and could have exploded', Home Secretary Theresa May said on Saturday.

Although she said Britain was not thought to be a target, she also announced a ban on all unaccompanied cargo coming from Yemen into the country.

'Our preliminary investigation is now complete. I can confirm that the device was viable and could have exploded,' May told reporters following a meeting of the government's emergency committee, Cobra.

'The target may have been an aircraft and had it detonated the aircraft could have been brought down.

'We do not believe that the perpetrators of the attack would have known the location of the device when it was planned to explode.' The discovery of the British package on Friday and another in Dubai caused a major international security alert and US President Barack Obama said they represented a 'credible terrorist threat'. Ms May said on Saturday there were no plans to change Britain's threat level, already at its second highest level, suggesting an attack is highly likely.

But she said 'further precautionary measures' were needed and said that all unaccompanied cargo from the Yemen would be banned from Britain.

Device could have exploded