Indian authorities circulated sketches yesterday of three suspects believed to be behind a series of bombings outside courthouses in three cities that left at least 13 dead and more than 40 wounded.
Police said the blasts in northern Uttar Pradesh State on Friday afternoon were targeting lawyers.
They are questioning the owner of an Internet cafe in connection with a threatening e-mail sent just before the blasts occurred, media reports said.
"Now the Islamic raides [sic] which is going to take place against lawyer within minutes," said the message received by television news channels, the Indian Express daily said yesterday.
The message also accuses lawyers in the state of beating up people falsely accused by the police of terrorism, adding that the advocates "refused to take their cases and didn't allow others to take their cases."
The attacks came a week after the Uttar Pradesh bar council unanimously decided not to defend Islamist militants facing charges in the state.
The e-mail warned that Indian police would be targeted next, the Indian Express said.
Uttar Pradesh home secretary official Javed Ahmed said that sketches of three suspects had been released, but would not give further comment on the investigation.
"This is a terrorist attack on the advocates of our state," additional director-general of police Brij Lal said earlier, speaking by telephone from the Uttar Pradesh capital of Lucknow.
In the holy Hindu city of Varanasi, where nine people including three lawyers died on Friday, the state police chief said the blasts were similar to a series of recent explosions in the state.
"We will identify and zero in on the local modules of terror outfits," the Times of India quoted Vikram Singh as saying.
Four people were also killed in the city of Faizabad, near Ayodhya, a hotbed of Hindu-Muslim rivalry where Hindus tore down a 16th-century mosque in 1992 sparking riots that left 2,000 dead.
Singh said earlier that the bombs were transported to the courts of Varanasi -- where a string of explosions killed 23 people in March last year -- Faizabad and Lucknow by bicycles, which were then abandoned.
"The fact that three blasts took place at the same time ... it is clear that it is a conspiracy," India's junior home minister Sriprakash Jaiswal told reporters in New Delhi.
A bomb exploded last month at the important Muslim shrine of Ajmer, killing at least two.
Officials have said that militants target religious centers in an attempt to divide majority Hindus and minority Muslims.