British anti-terrorist officers searched a house and two workplaces on Saturday for traces of a possible chemical bomb they fear could be used in an attack in Britain.
The search followed a police raid on the house in the east of the capital a day earlier in which a 23-year-old suspect was shot and wounded.
Behind a wall of plastic sheeting, police scoured the house in an ethnically mixed area of east London for signs of toxins or explosives following a dawn raid at the property on Friday.
Police also carried out further "small searches" at the workplaces of two men detained in the raid that involved more than 250 officers, some dressed in chemical suits.
The suspect shot in Friday's raid was recovering under police guard in hospital on Saturday. The second suspect remained in custody at a high security police station in London.
"What we are looking for is some form of viable chemical device," a police source told Reuters of the search at the house.
"A device that would have a fatal effect on someone standing nearby both from the explosion and from the chemical it contained," the source said, adding that the device being sought was a type of conventional bomb surrounded by toxic material.
If no bomb was found, it was possible the device had been moved, someone else was hiding it, that it had never been built or that intelligence had been wrong, the source said.
Police have said nothing suspicious was found in an initial search of the house.
Police were granted an extension until Wednesday to question the two men, held "on suspicion of commission, preparation or instigation of acts of terrorism," police said in a statement.
Friday's operation, one of the biggest since last July's suicide bombings on the capital's transport network, was prompted by suspicions that the house could have been used for making bombs or chemical weapons.
Police also detained a neighbouring family but freed them without charge.
Asan Rehman, a spokesman for the family, told Reuters the two men still in detention were brothers, were Muslims and of Bangladeshi origin. Neighbours described them as friendly and "very religious".
The failure by police to immediately find any evidence of criminal activity sparked anger among the large Muslim population in the Forest Gate area of London, who said they were being deliberately targeted and accused the police of shooting first and asking questions later.