A spokeswoman for city emergency officials says firefighters were called to extinguish the small fire on the bus. She says a suspicious package was found on the bus. Police say engine trouble likely caused the fire.
The No. 205 bus was traveling on Gray's Inn Road, near King's Cross station.
Meanwhile, officers continued questioning 20 suspects held in Britain in connection with the botched July 21 bomb attacks on London's transit system, including two men arrested in raids in south London late Monday. The government said it was trying to extradite from Rome one of the suspected attackers; Italy also arrested two brothers of that suspect.
Italy's bringing its own terrorism charges against the suspect, which will likely lead to tangled issues there, reports CBS News correspondent Charlie D'Agata. Lawyers representing Osman Hussein — also known as Hamdi Isaac — said they will fight the extradition.
British police are investigating possible links between the terror cell that killed 52 people when it bombed three Underground trains and a red double-decker bus on July 7, and a second cell that targeted the same transportation system two weeks later but caused no deaths when their bombs failed to fully explode.
Police say the four suicide bombers who carried out the July 7 attacks are all dead. And they believe they have arrested all the failed July 21 bombers.
On Tuesday, Underground officials restored full service on the Hammersmith and City line and the District line, which were partially shut down after the July 7 bombing at Edgware Road station.
Two other lines still remain closed or suspended.
British Transport Police continued its highly visible policing operation across the capital's subway system and overland rail network on Tuesday, spokesman Simon Lubin said. Officers in bright yellow jackets were posted outside many stations, although the police presence was not as strong as on Thursday, when a massive force patrolled the network exactly three weeks after the first attacks and one week after the second attempt.
Home Office minister Hazel Blears also planned the first in a series of meetings with representatives of Britain's Muslim community amid increasing complaints that young Muslims were being targeted by police in stop-and-search operations.
"Just picking people up on the basis that they are Muslim is never going to get the results that we want," Blears told the British Broadcasting Corporation's Radio 4 on Tuesday, reversing her earlier support for the controversial police initiative. "Tackling terrorism is absolutely dependent on the confidence of these communities to feel that they can come forward, give information and be part of the fight against this threat."