A second man has been arrested in connection with Thursday's attempted bombings in London, police said.
Police have linked these men to the failed London bomb attacks
The man was arrested under anti-terror laws in Stockwell, south London, late on Friday night.
A man held in an earlier police raid at Stockwell is still being questioned. A man was shot dead by police at nearby Stockwell Tube station on Friday.
Pictures of four men sought over the failed attacks on three Tube trains and a bus have been released by police.
The Hammersmith and City line Tube train targeted by Thursday's bombers has been moved and cordons around Shepherd's Bush station removed.
Metropolitan Police Commissioner Sir Ian Blair declined to say if the men arrested in Stockwell were any of the men pictured.
He urged the public to be vigilant and mind their bags on transport systems, but to go about their business as normal.
As part of the police's standard procedure, the Independent Police Complaints Commission (IPCC) is investigating the Stockwell shooting.
Sir Ian said the shooting was "directly linked" to the ongoing bombs investigation.
Meanwhile, police are dealing with a security alert in west London.
A suspicious package was found in a park near White City and police have cordoned off a section of the A40 and Scrubbs Lane.
Earlier, Mile End Tube station in east London was closed after a reported sighting of one of Thursday's bombers. It reopened 30 minutes later and no arrests were made.
The dead man, who was under police observation, was shot at about 1000 BST on Friday after apparently refusing to stop as he entered Stockwell station.
Eyewitnesses say he was chased on to a train where officers bundled on top of him and shot him in the head.
Police cordoned off a 200-metre area around the station
Police have said it is not yet clear if he was one of four bombing suspects but BBC correspondent Danny Shaw said the man was believed to be an accomplice of the men.
The Muslim Council of Britain said they were concerned about a possible police "shoot to kill" policy.
But Pc Norman Brennan, head of the Protect the Protectors group, said the recent attacks proved all officers should be armed.
Anyone with information about the shooting can call police on 020 8785 8632.
The men arrested in Stockwell are being held at Paddington Green station, central London, on suspicion of the preparation, instigation and commission of acts of terrorism.
The first man arrested was held during a raid at a block of flats between Carroun Road and Dorset Road at about 1630 BST by armed police. He was led away with a woman and child.
Meanwhile, a 29-year-old West Yorkshire man, held since 12 July on suspicion of terrorist offences, has been released without charge.
Sir Ian Blair said the failed attacks and the carnage on 7 July left Scotland Yard facing "the greatest operational challenge" in its history.
Three devices found after the failed bombings were the same size and weight as those used on 7 July.
The fourth was smaller, apparently contained in a plastic box. The same chemicals appear to have been used.
They targeted Oval, Warren Street and Shepherd's Bush stations and a bus in Hackney.
1: Witnesses report seeing up to 20 plain clothes police officers chase a man into Stockwell Tube station from the street
2: One person says the man vaulted the automatic ticket barriers as he made his way to the platforms
3: The most direct route is via this escalator or the staircase that sits alongside it
4: Police challenge the man but he apparently refuses to obey instructions and after running onto a northbound Northern line train, he is shot dead