The party also said the Bihar government was "soft on terror".
"The kind of incident that happened in Patna, I believe it is due to terrorist activities," BJP president Rajnath Singh said Monday.
"The incident is unfortunate, certainly there were intelligence and security lapses, because of which the incident occurred," he said.
Leader of Opposition in the Rajya Sabha Arun Jaitley said the blasts came as a reminder of "vulnerability", as mass gatherings occur in the run-up to elections.
"These blasts are a grim reminder of the vulnerability of the security of both senior leaders and political events being organised in the run-up to the elections," Jaitley said.
"India cannot afford to be either soft on terror or soft on security. A policy against terror and the need for security cannot be relatable to the policy of vote bank politics of a given government," he said.
Six people were killed and over 80 injured Sunday in a string of explosions that took place at Patna railway station and Gandhi Maidan, shortly before BJP's prime minister candidate Narendra Modi spoke at a rally.
Rajnath Singh lauded the people of Bihar for being patient when the blasts occurred.
"I want to thank the people of Bihar who displayed such patience, I appreciate it," he said.
He added that Bihar Chief Minister Nitish Kumar called him Sunday night and assured him that action would be taken.
Party leader Shahnawaz Hussain said the Bihar government failed to follow its "Rajya Dharma" (the duty of the rulers).
"It's the duty of the government to provide security to all rallies, regardless of the party organising it. The Bihar government failed to follow its 'Rajya Dharma'," he said.
In Patna, BJP leaders accused Nitish Kumar of "deliberate security lapses".
"It was not mere negligence, (but) deliberate security lapses," former deputy chief minister Sushil Kumar Modi said, claiming this was because Nitish Kumar is not treating Narendra Modi as a political opponent but as a "political enemy".
"It is a serious matter... Nitish Kumar will have to explain to people about the security lapses," he said.
Leader of Opposition in the state assembly Nand Kishore Yadav questioned Nitish Kumar's statement that there was no intelligence input.
"The IB (Intelligence Bureau) alerted Bihar government on Oct 23 about a likely blast in Modi's rally. But the state government ignored it," he alleged.