Pakistani security forces detained 25 suspected Islamist militants in a series of raids linked to investigations into the bomb attacks in London.
The latest detentions were made in an overnight crackdown in the province of Punjab and included members of outlawed Islamist groups.
"They are being questioned for links with any of the bombers," an official of the provincial government said. The official said security agencies had detained the 25 suspects in the cities of Dera Ghazi Khan, Multan, Faisalabad and Khushab.
A security official in Punjab said he expected that questioning of a handful of other suspects detained in recent days in the provincial capital, Lahore, would confirm ties to the London bombers.
"We suspect two or three of the detained (from Lahore) had links with the bombers. We are interrogating them intensively. We hope we will come out with some positive outcome shortly," he said.
Three of the four bombers were young British Muslims of Pakistani descent, and officials say all of them entered Pakistan through the southern city of Karachi last year. The fourth attacker was a Jamaican-born Briton.
A security official said one suspect arrested yesterday in Lahore had been found with explosives and large amounts of cash.
The death toll from the London Underground train and bus bombings stood at 56 today.