Bahraini police have arrested three suspects over "terrorist activities" after seizing materials that can be used to manufacture explosives, the public security chief said on Wednesday.
Major General Tariq al-Hassan said in remarks to the press that police are still searching for three other suspects.
"Bahraini police and Scotland Yard are investigating the issue," Hassan said.
Following a raid on a residential area in a Shiite village, "police have seized more than five tonnes of materials that could be used to manufacture explosives," he added.
Hassan acknowledged, "some police officers could have acted inappropriately," after the Shiite opposition accused the public security of abuse.
"Any officer that is found guilty of violating appropriate procedures will be punished," he said.
"Such abuses, if they are proved, are unacceptable. They contradict the mission of the interior ministry."
Hassan said 10 out 14 complaints against police and the ministry "have been referred to competent authorities, including the courts. The other four are still being probed."
In July, more than 240 people were arrested, while dozens were hurt in clashes with the police, the main Shiite opposition group, Al-Wefaq, said.
The authorities accuse young Shiite protesters of using petrol bombs against security forces during frequent demonstrations in villages outside the capital Manama.
Sporadic and small demonstrations have intensified in the villages since a March 2011 crackdown ended month-long protests in Manama's main Pearl Square demanding democratic reforms in the Sunni-ruled Shiite-majority Gulf state.
Human rights watchdog Amnesty International says 60 people have been killed since the protests first erupted in February last year