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 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 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'.

The authorities accuse young protesters of using petrol bombs against security forces during frequent demonstrations in villages outside the capital Manama.