A raid on an east London house where anti-terrorist police arrested two brothers was prompted by fears one suspect had built an explosive device that could release a toxic chemical gas, British police said Saturday.

Officers — many wearing protective clothing — carried out a meticulous search of the row house in seeking evidence of a bomb, police said. They also were searching the two men's workplaces — a supermarket and a postal office.

"We don't know yet if there is a device, but it is the focus of our searches and of the intelligence we had," a police official said, speaking on condition of anonymity because of the sensitivity of the operation.

CountryWatch: United Kingdom

"Intelligence indicated it may have a chemical component, possibly involving a toxic gas," the official said.

In the raid on Friday, police shot and wounded one of the brothers in the shoulder.

Both brothers had criminal records, but had not previously been examined by anti-terrorism officials, the police official said. The two suspects were not believed to have links to the deadly July transit network bombings in London, or to any other known terrorist plot in Britain, the official said.

A judge signed a warrant for police to hold the two men in custody until Wednesday, giving extra time for police to question the men. Police can apply for a further extension next week if needed.

The wounded man, 23, was under guard at the Royal London Hospital, and was expected to be released Sunday, while his 20-year-old brother was being held on suspicion of terrorism and questioned at the high-security Paddington Green police station in north London, police said.

Officers on Saturday searched the men's work places — one in Tottenham, north London, and another in Whitechapel, east London.

Kate Roxburgh, lawyer for the injured man, said he denied any involvement in terrorism, and said he was "lucky to still be alive."

"He wasn't asked to freeze, given any warning and didn't know the people in his house were police officers until after he was shot," she said.

Lawyer Julian Young said the younger man also denied any involvement in terrorism.

The Independent Police Complaints Commission said an inquiry into the shooting has begun, as is standard procedure in Britain.

The lawyers and neighbors said the two suspects were British-born Muslims and brothers — but police have refused to confirm any details about the suspects.

Peter Clarke, head of the anti-terrorist branch of London's Metropolitan police, said Friday's raid had been in response to information about a "specific threat" which "demanded an intensive investigation and response."

About 300 police, some armed and some wearing protective chemical, biological and radiological suits and acting with the advice of biochemical experts — were deployed in one of the largest raids in the capital since the deadly bombings of London's transport network in July, which killed 52 commuters.

However, residents voiced anger Saturday at what they claimed were heavy-handed police tactics.

A family living next door to the raided property said it had been detained by officers, and that one man had received injuries. The three men, a woman and an 8-month-old baby were held for 12 hours before being released without charge, they said in a statement.

"We are completely innocent and in no way involved in any terrorist activity," the family said in a statement, issued through a community group, the Newham Monitoring Project.

Clarke said forensic examinations at the house could continue for several days.

Neighbors said a man, a woman and their four teenage children lived in the raided address. They said the wounded man had worked for the postal service.