"One woman died and four were injured in the first blast," Bangalore police commissioner Shankar Bidri told reporters, adding the total amount of explosive used in the bombs was "equivalent to one or two hand grenades."

"We suspect that timer devices were used in two or three explosive devices, while the others could have been set off using mobile phones," he said.

"We are investigating the blasts. Bomb disposal squads and forensic experts have reached the spot. Bangalore police is on high alert."

India's Home Secretary Madhukar Gupta said there were a total of seven blasts within a radius of 10 to 15 kilometres (six to nine miles).

Assistant police commissioner A. Raghuveer said the bombs went off within minutes of each other in different parts of the city, the hub of India's outsourcing and software industry and the Indian base of many global technology firms.

"Initial reports say that some of the blasts are low intensity using gelatin (gelignite explosive) sticks," Raghuveer told reporters.

One blast was in the business district, while the others were in the southern suburbs of the religiously mixed and cosmopolitan city, the capital of Karnataka state, police said.

"Such incidents will not deter the government from pursuing its policy of dealing with anti-national elements in a resolute manner," Indian Home Minister Shivraj Patil was quoted as saying by the Press Trust of India news agency.

Bangalore is home to more than six million people and some 1,500 domestic and foreign firms -- including Infosys Technologies, the pioneer of India's outsourcing sector.

Soon after the blasts, the IT companies downed their shutters and asked their employees to go home, a representative for the software companies told AFP.

Bangalore has been relatively free of the militant attacks that have plagued other parts of the country, although one person was killed and four wounded in an Islamist attack at a premier science institute in the city in December 2005.

Intelligence sources said it was too early to say who may have been behind Friday's attacks.

"We are looking at the pattern of the explosions, and are trying to work out who is behind them and why," a federal Intelligence Bureau official told AFP. "We hope to find out very soon."