A series of low-intensity bombs exploded on Sunday in the northeastern city of Patna, apparently targeting a vast rally featuring the opposition leader Narendra Modi, whose Bharatiya Janata Party hopes to unseat the long-dominant Congress Party in national elections next spring.
Homemade bombs, fitted with wires and timers, exploded in a series of crowded places: at a railway station, outside a movie theater, near two landmark buildings, and two on the Gandhi Maidan grounds, where Mr. Modi was preparing to speak, according to Abhayanand, the state's director general of police.
Four people were arrested Sunday afternoon, said Manu Maharaj, Patna's district police chief. He said that one man was arrested at the scene of a blast and confessed to being involved, and that all four men in custody were being interrogated.
Bharatiya Janata Party officials had hailed the rally as the largest to be held in the state of Bihar, a high-stakes electoral battleground, and decided to proceed despite the blasts. An enormous crowd roared in response as Mr. Modi invoked the Hindu epics, asking them to chant traditional battle cries.