Indian investigators are sifting through hours of police interrogations in search of information about the people behind Tuesday's train bombings that killed around 180 people and wounded at least 700 others.
Media speculation has focused on three men as top suspects, but Mumbai police chief A.N. Roy says no suspect has been officially named or arrested. He said hundreds of people have been questioned.
Pakistan has rejected allegations by Indian Prime Minister Manmohan Singh that the bombers responsible for the seven train blasts were supported by elements from across the border.
However, Indian officials said Saturday that plans for high-level peace talks next week with Pakistan have been thrown into doubt because of the train bombings.
In New York Friday, U.S. Assistant Secretary of State Richard Boucher urged the peace process between the two nuclear-armed neighbors to continue.
The United States says if the Indian investigation shows Pakistani-based militants were involved, both countries should work together to stop the terrorists.
After visiting victims of the blast in two Mumbai (previously known as Bombay) hospitals, Mr. Singh said it would be "exceedingly difficult" to move ahead with the peace process if Pakistan does not control terror groups mounting attacks in India.
The South Asian rivals began a peace process in 2004 after coming to the brink of war in 2002 over Indian accusations that Islamabad supports terror groups operating in Indian Kashmir. Tensions have eased, but there has been little progress in resolving the major point of dispute between them - Kashmir.