The arrests, in Tooting in south London, came a day after the seizure in Birmingham of Yassin Hassan Omar, 24, a Somali man suspected of being one of the four men who took part in the attacks. The arrest of Mr. Omar, who was being questioned by police today in central London, was the most important breakthrough so-far in the investigation into the London terror bombing campaign.
Three other men were arrested Wednesday in a second house in Birmingham, about 120 miles, north of London, and were held there.
Later Wednesday, houses were raided in Finchley and Enfield in north London, and police raided a house near Stockwell tube station in south London where they arrested three women under anti-terrorism laws.
London's transportation system was on precautionary high alert today with police standing guard at subway stations, three weeks after the July 7 bomb attacks on three trains and a bus. The attacks killed 56 people including the four suicide bombers.
The arrests come a week after the failed bomb attacks on three London subway trains and a bus. Despite the arrest of Mr. Omar, who is suspected of planning the failed attack on Warren Street station, the police said that they still do not know where the three other bombers are and the identity of two of them. However, on Wednesday they issued a new photograph of the unidentified man suspected of planning an attack on Shepherd's Bush station last Thursday.
The nine men arrested in Tooting today were not believed to include any of the three bombers who are still at large. Early reports suggested police raided a flat above a Turkish kebab shop and took away three men, believed to be of Turkish origin. Six other men were arrested from a nearby property opposite Tooting Broadway station.
Rajakumar Rajalingam, 28, who runs a 24-hour convenience store next to the restaurant, said dozens of officers raided the property at 4:30 a.m.
"Police stopped me outside my shop," he said. "They didn't allow me to get in. They said they have to raid the kebab shop next to mine and the flat on top of the shop. I saw 25 policemen armed with machine guns. At 5.30 they arrested three people who were in the kebab shop. I know one of them for more than two years. He is from Turkey and in his mid-40s. The police searched the flat upstairs."
The owner of the restaurant, Ahmet Ali, said: "Police told me I couldn't open the shop." He said: "Three of my employees who work in the shop during the nighttime use one room in the flat to sleep there." The police had arrested all of them, he said.
The arrests follow the capture of Mr. Omar, in the Small Heath area of central Birmingham, in a pre-dawn raid Wednesday. The police used a stun gun to subdue him after he scuffled with officers.
The police evacuated about 100 homes on the tree-lined street where Mr. Omar was staying. Bomb disposal officers were called to examine a suspicious package there.
The arrests widened the scope of the terror investigation to yet another major British city. They also focused scrutiny on an East African connection.
The police are searching for Muktar Said Ibrahim, a 27-year-old originally from Eritrea, whom they believe was also a would-be bomber.
The British police identified him and Mr. Omar, 24, as suspects in the attacks of July 21, circulating photographs of them and two other suspects that were taken by security cameras on the London subway and bus system.
Sir Ian Blair, chief of the Metropolitan police, warned the British public that the failure of the attacks on July 21 "should not be taken as some indication of weakening of the capability" of the bombers. "This was not the B-team. These were not amateurs," he said.
"I am confident that we will identify and find the bombers responsible," he said. But he said it remained possible that the bombers would strike again.
Prime Minister Tony Blair said in London on Wednesday: "We are greatly heartened by the operations today."
"It's an important development," the prime minister said.
The arrests in Birmingham came on a day of intense police activity that included the detention of a man at Luton Airport before he boarded a plane to Nîmes, in southern France. He was later released.
Late Tuesday, the police removed two men from a train in Lincolnshire, in the British Midlands, and held them under the Prevention of Terrorism Act.
The train was headed to King's Cross station in central London.
On Wednesday, the Lincolnshire police said they had no connection to terrorism and released them.
No arrests were made at the two properties in Enfield and Finchley, but the police were carrying out forensic examinations.
On Tuesday, officials at Scotland Yard said they had found traces of explosives at an apartment in North London, where one of the suspected July 21 bombers lived. Chemicals were also found in the garage of the complex.
The three women were arrested in Stockwell after a raid at about 6 p.m. on Wednesday evening on a flat at Blair House, close to Stockwell station in south London, the BBC said.
As the investigation unfolded, the body of a Brazilian man fatally shot Friday by the police in a London subway train was scheduled to be sent home to his family.
The shooting has put pressure on the police, who follow a shoot-to-kill policy with suspected terrorists.
In a television interview, Sir Ian said there had been 250 incidents since July 7 in which police believed they were pursuing a suicide bomber.
Seven came close to ending like the case of Jean Charles de Menezes, the Brazilian electrician who was shot in the head seven times and once in the shoulder in a station in south London.
"I know that when I last saw it, there had been seven times when we got as close to calling it as 'that' and we haven't," Sir Ian said.
In a related development Wednesday, the police released a man who was arrested last week after the attacks of July 21, The Associated Press reported.
The police said in an announcement that a man they identified as "A" had been released and "no further action would be taken" against him.
Another four suspects arrested between Friday and Monday remained in custody, the announcement said.
The man's identity was not released, but the police said he had been arrested Friday in London's southern Stockwell neighborhood.