Singh spoke to Bihar Chief Minister Nitish Kumar over telephone and asked him to investigate the matter.
He urged the people of the state to maintain peace and calm.
"Prime Minister condemns the blasts which occurred at several places in Patna today. He appeals to the people to maintain peace and calm," the Prime Minister's Office (PMO) tweeted on Sunday.
"PM Dr Singh talks to Bihar Chief Minister Shri Nitish Kumar and asks him to speedily investigate the blasts, and punish the perpetrators," it said.
At least one person was killed and 20 others were injured as a series of low-intensity blasts rocked Bihar's Patna city ahead of Bharatiya Janata Party (BJP)'s prime ministerial candidate Narendra Modi's rally on Sunday.
Five low-intensity blasts occurred in the city on Sunday, reports said.
According to reports, at least one person was killed as a crude bomb exploded in Patna railway station earlier in the day.
It was the first blast that rocked the city ahead of Modi's 'Hunkar Rally' in Patna.
Other blasts occurred around Patna's Gandhi Maidan where over 25,000 people had already gathered by then to attend Modi's rally.
The police have detained one person so far.
--IBNS (Posted on 27-10-2013)