Security has been heightened in the Indian city of Bombay after a bomb explosion ripped through a bus, killing three people and injuring more than 40 others.
Extra security is also in place in the capital, Delhi, with police roadblocks set up and checks on public transport.
The blast occurred near a telephone exchange at Ghatkopar - a north eastern suburb India's of financial capital, also known as Mumbai late on Monday night.
This is the fifth bomb blast in Bombay in recent months, three of which targeted the city's public transport system.
On Tuesday, police in Bombay said they had declared a "high alert" in the city and elsewhere in the state of Maharashtra.
"We have stepped up security at all the key areas and installations of the city and increased vehicular checking at various entry points of the city and the state," joint police commissioner Ahmed Javed was quoted as saying by the AFP news agency.
An investigation is currently under way and forensic experts have been examining evidence gathered at the blast site.
Bombay Police Commissioner RS Sharma said he suspected Pakistan's Lashkar-e-Toiba Islamic militant group of carrying out a bomb attack.
Mar 2003 - 11 killed in commuter train
Jan 2003 - 30 injured in market attack
Dec 2002 - 23 injured at McDonald's outlet
Dec 2002 - Two killed in bus blast
Mar 1993 - More than 250 killed in serial blasts
"We suspect it could be the work of Lashkar-e-Toiba and we have commissioned an enquiry," he said.
Lashkar-e-Toiba is one of the two Pakistani rebel groups that Delhi blames for the December 2001 militant attack on its parliament which left 15 people dead, including five attackers.
Chagan Bhujbal, Deputy Chief Minister of the western Indian state of Maharashtra - of which Bombay is the capital - said the blast appeared to be similar to an earlier bomb explosion in the same area and those arrested at the time had links with Lashkar-e-Toiba.
Mr Bhujbal added Bombay's crowded buses and trains were being deliberately targeted.
The bomb was detonated at the rear of the bus run by the Bombay Electric Supply and Transport Undertaking.
The explosion tore open the roof of the bus, damaged nearby vehicles and shattered the windows of some buildings, police said.
Eleven people were killed in a bomb explosion on a Bombay commuter train in March.
Police linked it to another bomb blast in a Bombay suburb three months previously.
An Indian bus explosion in March killed 11 and injured 40
In May, Bombay officials announced they were planning an elite anti-terrorist police squad to bolster security.
The city was hit by serial bombings 10 years ago, in which more than 250 people died. Fifteen massive explosions rocked the length and breadth of Bombay on 12 March, 1993.
Underworld gangs were blamed for the attacks.