Bahraini authorities have arrested several people in connection with Tuesday's deadly bombing and suspect the attack was a "foreign attempt" to harm the Gulf state's stability, local media reported on Wednesday.
A published comment by Prime Minister Sheikh Khalifa bin Salman al Khalifa alleging a foreign role did not name any country, but Bahrain has frequently accused regional adversary Iran of trying to orchestrate bombings in the country.
Tehran dismissed suggestions it had a role in the attack.
Speaking about Tuesday's bombing, which killed two policemen and wounded six, Sheikh Khalifa said Bahrainis' patriotism had "always foiled foreign attempts to interfere in the kingdom's internal affairs", the official Bahrain news agency reported.
"The Prime Minister reiterated categorical rejection of foreign interference, expressing deep regret over the martyrdom of two police officers," he was quoted as saying.
The bombing outside a girls' school in the Shia village of Sitra was the deadliest in U.S.-allied Bahrain since March 2014, when a blast killed three policemen.
It drew strong condemnations from fellow Sunni Muslim Gulf Arab states who share Bahrain's suspicion that Shia power Iran is seeking to foment instability in Arab lands.
Bahrain's interior ministry said the explosives used in the Sitra attack resembled some seized at the weekend, when authorities claimed they had foiled a plot to smuggle in arms and explosives from Iran.
Iran's Foreign Ministry dismissed that as "state media propaganda" and condemned the bombing.
"Terrorism and extremism are the main challenges facing the region," its spokeswoman Marzieh Afkham was quoted as saying by Iran's Press TV on its website.
Sunni-ruled Bahrain has long accused Iran of stirring up unrest among its Shia population and tension between the neighbours has risen in recent days, with Bahrain recalling its ambassador from Tehran on Saturday.
Tehran denies interference in Bahrain but openly supports opposition groups seeking greater rights for the Shia majority. Sporadic violence aimed at Bahraini security forces has become the norm since mass, Shia-led pro-democracy protests were put down by the government in 2011.