London bombs killed 'at least 50'
Sir Ian Blair said the final death toll was unlikely to top 100, but warned an unknown number of bodies remain in the blast-hit Tube train at Russell Square.
The police chief confirmed that 13 people were killed in the bus blast at Tavistock Square.
The police had an "implacable resolve" to track down those responsible for the bombings, the Met Commissioner said.
The blasts on three Tubes and a bus left 700 hurt, with 100 held overnight in hospital and 22 serious or critical.
It was "blindingly obvious" that a terrorist cell was operating in Britain, Sir Ian said, as massive intelligence operation to find the perpetrators moved into gear.
"This was an attack which was entirely arbitrary, random, irrespective of race, of colour of gender and age," he said.
Victims not only came from Britain but from Sierra Leone, Australia, Portugal, Poland and China, he said.
Politicians and police have paid tribute to the resilience of Londoners, with transport returning to a near-normal service on the Tube.
Speaking from the G8 summit in Gleneagles, and flanked by world leaders, the prime minister said the purpose of terrorism was to put anger and hatred in people's hearts.
But it would not succeed, he said, adding that the only hope was the alternative to such hatred.