The Boston marathon bombs were explosives packed in 6-litre pressure cookers and placed in black duffel bags, according to a source close to the investigation.

US President Barack Obama has said they do not know who carried out the Boston marathon bombings or why.

Police and the FBI have raided a number of homes in Boston in the hunt for those responsible for the explosions at the Boston Marathon.

The full might of America's police and security services was today focused on finding out who planted the Boston Marathon bombs, and why.

Former CIA director David Petraeus was sneaked into the Capitol today, away from the media, to face lawmakers’ questions about the attack on the US Consulate in Libya – just one week after he resigned over an extramarital affair.