At least six bombs exploded in the heart of New Delhi in September [AFP]
A chronology of some of the biggest attacks in India in the 21st century.
December, 13 2001 - Indian parliament in Delhi is attacked and 12 people are killed as then prime minister Atal Behari Vajpayee vows to wage a "do or die" war against "terrorism.
March 13, 2003 - Bomb attack on a commuter train in Mumbai kills 11 people.
August 25, 2003 - Two car bombs kill about 60 people in Mumbai.
August 15, 2004 - Bomb explodes in the northeastern state of Assam, killing 16 people, mostly schoolchildren, and wounding dozens more.
October 29, 2005 - Sixty-six people killed when three blasts rip through markets in New Delhi.
March 7, 2006 - At least 15 people killed and 60 wounded in three blasts in the northerly Hindu pilgrimage city of Varanasi.
July 11, 2006 - More than 180 people killed in seven bomb explosions at railway stations and on trains in Mumbai that are blamed on an Islamist group.
September 8, 2006 - At least 32 people killed in a series of explosions, including one near a mosque in Malegaon town, 260km northeast of Mumbai.
February 19, 2007 - Two bombs explode aboard a train heading from India to Pakistan. At least 66 passengers, most of them Pakistanis, burned to death.
May 18, 2007 - A bomb explodes during Friday prayers at an historic mosque in the southern city of Hyderabad, killing 11 worshippers.
August 25, 2007 - Three co-ordinated explosions at an amusement park and a street stall in Hyderabad kill at least 40 people.
May 13, 2008 - Seven bombs rip through crowded streets in the western city of Jaipur, killing at least 63 people in markets and outside Hindu temples.
July 25, 2008 - Eight bombs explode in the city of Bangalore, killing one woman and wounding at least 15 other people.
July 26, 2008 - At least 16 bombs explode in Ahmedabad in the state of Gujarat, killing 45 people and wounding 161. The "Indian Mujahideen" claims responsibility for the attack and the May 13 bombings in Jaipur.
September 13, 2008 - At least six bombs explode in crowded markets and streets in the heart of New Delhi, killing at least 18 people and injuring scores more. The Indian Mujahideen again claim responsibility.
October 30, 2008 - A series of apparently co-ordianted bomb blasts in three districts of northeastern Assam state kill at least 20 people.
November 26, 2008 - Heavily armed men attack high-profile hotels and restaurants in Mumbai, killing at least 101 people and taking US and British nationals hostage, among others.