Only 11 were detained, all for petty crimes unrelated to the bombings, said senior police inspector Joseph Gaikwad. The 11 were not thought to have been involved in the attacks, but police believed they may have information about the bombers.

Police have carried out several such sweeps since Tuesday's attacks, which killed more than 200 people. Saturday's house-to-house searches were conducted mainly in the slums of Mumbai's Mahim neighbourhood, an area popular with illegal immigrants from Bangladesh.

"This was a routine combing exercise. We have questioned and released all but 11 of the 307 who were brought in from Mahim," Gaikwad said.

The sweeps came a day after Prime Minister Manmohan Singh said the bombers had support from inside Pakistan, warning that a peace process between the nuclear-armed rivals could be derailed unless Islamabad reins in terrorists.

Singh's unusually blunt comments appeared to signal an abrupt shift in relations between India and Pakistan, whose ties had warmed over the past two years. Pakistan Foreign Ministry spokeswoman Tasnim Aslam dismissed India's allegations as "unsubstantiated."

Initial fallout came quickly, with talks between the foreign secretaries of India and Pakistan planned for July 20 cancelled, Indian media reported Saturday.

Singh told reporters Friday that investigators were certain that terror cells operating in India "are instigated, inspired and supported by elements across the border, without which they cannot act with such devastating effect."

Singh noted that Pakistan had assured India two years ago that its territory "would not be used to promote, encourage, aid and abet terrorism."

"That assurance has to be fulfilled before the peace process and other processes progress," he said.

After coming to the brink of war in 2002, India and Pakistan began a peace process that has brought them closer, yet concrete agreement on the most pressing issue the Himalayan region of Kashmir has been minimal.

Investigators have cast a wide net for the Mumbai bombers, focusing on the Kashmiri Lashkar-e-Tayyaba militant group, along with smaller homegrown organisations. Lashkar, based in Pakistan, has denied involvement.

Police have named three men wanted in the bombings Sayyad Zabiuddin, Zulfeqar Fayyaz and a man known only as Rahil but released few details about them. Indian news reports said all three were members of Lashkar-e-Tayyaba.