Bahrain has been seen sporadic protests since 2011, with increasing use of explosives
A policeman was killed while on duty southwest of the Bahraini capital Manama on Monday in what authorities described as a "terrorist" attack using a bomb made by Hezbollah.
The Interior Ministry gave few details of the incident in the village of Damistan. Bahrain's Foreign Minister, Sheikh Khaled bin Ahmed al-Khalifa, said on Twitter the policeman had fallen victim to "a bomb made by the terrorist Hezbollah".
He was referring to the Lebanese Shi'ite guerrilla group, which Bahrain has previously accused of being linked to Shi'ite militants in the country.
Hezbollah has been vilified by Sunni Muslims over its participation in Syria's civil war alongside President Bashar al-Assad and against Sunni-backed rebels fighting to oust him.
Witnesses in Damistan said police cordoned off the area and were searching for evidence.
The Sunni Muslim-ruled island kingdom, home to the US Fifth Fleet, was swept by protests in 2011 led by majority Shi'ites demanding political reforms.
Bahrain has accused Shi'ite power Iran of fomenting the unrest, a charge Tehran has denied.
Since 2011 more protests have erupted sporadically and there have been a growing number of attacks using explosives. In March, three policemen were killed by a remotely-detonated bomb.
Two policemen were injured last month by a bomb in the Shi'ite village of Deraz west of Manama.
In November Bahrain held parliamentary elections, boycotted by the opposition which complained that changes to the voting districts would favour the Sunni Muslim minority represented by the ruling family.