"Terrorist blast in police bus near Jua village. 4 policemen injured and they are in a stable condition. Necessary steps are being taken," the ministry said on its Twitter account.
It gave no further details.
On January 1, gunmen attacked the prison in Jaw, killing a policeman and allowing 10 inmates to escape.
Shiites convicted over anti-government protests in Sunni-ruled Bahrain were held at Jaw.
Tiny but strategic Bahrain, home to the US Fifth Fleet, has been rocked by unrest since the authorities crushed Shiite-led protests in 2011 demanding a constitutional monarchy and an elected prime minister.
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One of those on trial is Sheikh Issa Qassem, the country's Shiite spiritual leader.
He was stripped of his citizenship last year for "serving foreign interests" -- a reference to Shiite Iran.
Today, clashes broke out between security forces and protesters in several Shiite villages as a new hearing in Qassem's case was underway, witnesses said.
Protesters chanted anti-government slogans and carried portraits of Qassem, they said.
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