As the air travel chaos caused by the scare eased, Pakistani officials said they had helped unravel the conspiracy arresting last week seven people, including two Britons of Pakistani origin.
The Pakistani foreign ministry named one of them as Rashid Rauf, adding that there were "indications" of an "Afghanistan-based Al-Qaeda connection".
US reports suggested another five suspects remain at large, after British police swooped hurriedly on 24 people in the UK late Wednesday and in the early hours of Thursday.
One of the 24 suspects was released yesterday without charge, as police obtained warrants to hold onto 22 others until next Wednesday. The 23rd individual is to remain in custody until a court hearing on Monday.
In Italy, 40 people were arrested in raids on Thursday and Friday at various locations "frequented by Islamists," the interior ministry in Rome said.
Newspapers in London cited British government sources saying the operation swung into action overnight on Wednesday after a message sent from Pakistan after the arrests there apparently urged the plotters to go ahead.
In London, the Bank of England has frozen the accounts of 19 of the suspects arrested in Britain and disclosed their names, virtually all of them Muslim, apparently of Pakistani origin.
US officials say the conspiracy, which they consider the most serious since the September 11, 2001, attacks in New York and Washington, would have seen the perpetrators smuggle seemingly innocuous liquids in drinks bottles or other containers onto US-bound planes from Britain.
Once on board, they would be assembled into bombs of liquid explosives.
The Evening Standard newspaper said tickets for United Airlines flights yesterday and next Wednesday were seized during the raids.
US Homeland Security chief Michael Chertoff suggested that explosives had been recovered at the homes of arrested suspects in Britain, while The Times newspaper said a "martyrdom video", seemingly recorded by a would-be suicide bomber, was found.