London Police Commissioner Ian Blair says he expects the final death toll from Thursday's bus and subway bombings to be fewer than 100.

Authorities say the number of deaths now exceeds 50, with more than 700 wounded.

Mr. Blair said Friday that 13 people died in the blast that tore open a double-decker bus. He said some bodies had to be left on wrecked underground trains while engineers worked to ensure the safety of the tunnel. Meanwhile, investigators sifted through the debris for clues to who carried out the attacks.

The commissioner told reporters the bombs were all quite small, about four kilograms, and said there was no indication they were suicide blasts. But he added he could not rule that out.

Earlier, Mr. Blair said the attacks had all the hallmarks of the al-Qaida terrorist network, but he predicted a long and complex probe. A previously unknown "Secret Group of al-Qaida's Jihad in Europe" claimed responsibility on an Arabic-language website soon after the blasts.

Some information for this report provided by AP, AFP and Reuters.