Indian police are continuing their hunt for those behind Tuesday's bomb attacks on commuter trains in Mumbai, in which some 200 people were killed.
Mumbai is slowly returning to normal
Police have questioned hundreds of people and one person was detained in the southern state of Andhra Pradesh.
But police have denied reports they released sketches of any suspects.
A Muslim organisation banned in India, the Students' Islamic Movement (Simi), is the latest group to deny involvement in the attacks.
The home minister of the state of Andhra Pradesh, K Jana Reddy, told reporters that a man on a train in Hyderabad - identified as Abdullah - was held in connection with the bombings.
So far no formal arrests or charges have been reported in Mumbai, formerly known as Bombay.
Police have carried out a series of raids in the city and other parts of the state of Maharashtra amid tightened security.
About 300 people were detained for questioning, but police said the detentions were routine, and many of those questioned have now been released.
At a news conference in the capital Delhi, a Simi leader, Shahid Badr Falahi, described the attacks as deplorable and said his organisation had no part in them
Activists of Simi were allegedly involved in bomb blasts in Mumbai in 2003, when 55 people were killed. They are currently being tried in a special court in the city.
Police and the top bureaucrat in Maharashtra state, DK Shankaran, have said the attacks have similarities with previous attacks committed by Lashkar-e-Toiba, a leading Pakistan-based militant group fighting in Kashmir.
But the group has not been directly accused, and has strongly denied any involvement.
Meanwhile, Pakistan's foreign minister has reacted angrily to suggestions his country could be to blame for the train bombings.
Khurshid Kasuri said India should be careful about linking the attacks to militants based in Pakistan.
He was speaking after India's foreign ministry called on Pakistan to take action against militants operating from its territory.
Mr Kasuri rejected any Pakistani link to the blasts.
"You can't really blame everything on Pakistan; it's very unfair," the Pakistani foreign minister told the Associated Press news agency during a visit to the US.
He condemned "unreservedly the despicable acts" that took place in Mumbai.
Correspondents say that in the past India has been quick to blame Pakistan for providing a sanctuary for militants to launch such attacks from, but this time Delhi has adopted a more cautious approach.
Delhi has however urged Pakistan to "dismantle the infrastructure of terrorism" on territory under its control.