Police in London have said all three of the devices that exploded on underground trains in Thursday's attacks went off within seconds of each other.
The disclosure was made at a news briefing this afternoon at which the Metropolitan Police gave the latest details of their investigation of the bombings.
There are 49 confirmed fatalities and concern for 25 more people who are missing.
Deputy Superintendent Jim Dickie said none of the bodies had yet been identified.
Police also said emergency workers were facing a strong challenge in trying to recover bodies from the wreckage of a train near King's Cross station.
Rescuers are contending with extreme heat as they work to retrieve bodies still trapped underground.
The roof of a tunnel between King's Cross and Russell Square stations is said to be dangerously unstable and is slowing down efforts to reach a rail carriage believed to contain a number of bodies.
Earlier today, the British Prime Minister, Tony Blair, promised that his government will act with caution in the wake of the bombings and will not introduce authoritarian laws in response to them.
In a BBC Radio interview, Mr Blair also said the world would have to deal with the underlying causes of terrorism and that security alone could not provide complete protection.
Meanwhile, a huge forensic and intelligence investigation is continuing.
Hundreds of hours of CCTV footage have been gathered in an attempt to identify the bombers.
Forensic teams are working at the four bomb scenes to try to determine the type of explosives used in the attacks.