Three bombs planted by suspected Sikh extremists exploded within minutes of each other in India's neighboring northern states Tuesday, killing at least 17 people and injuring 64 others, police said. Police said security forces in the region were placed on top alert in case of further violence. Deputy Punjab Police Chief Sarabjit Singh said investigators believed all three bombs were set by members of the Babbar Khalsa, the most hard-line Sikh extremist group.