DHAKA, Feb 21 (Reuters) - Bangladesh police arrested four members of an underground Islamist group in a crackdown on Saturday, an officer said, a day after a suspected militant set off a grenade inside a police station wounding 10 people.

The militant and three other members of the Jamaat-ul-Mujahideen were being paraded before journalists along with weapons captured from them on Friday when he managed to grab and detonate a grenade.

Police and journalists were among the wounded in the incident in Gazipur, 30 km (20 miles) north of the capital Dhaka.

On Saturday police raided a suspected hideout near the site of the incident and arrested four more members of the Jamaat which has been waging a campaign for introduction of sharia law in Bangladesh.

A police officer said explosives were also seized from the hideout.

Police had tightened security across the country on reports that the group was planning to attack ceremonies marking a language anniversary on Saturday, he said.

The day marks the killing of students by police more than half a century ago for demanding Bengali to be made a state language in what was then East Pakistan.

The Jamaat suffered a setback in 2007 when six top commanders were hanged, but police and intelligence officials say their followers have been regrouping ever since and plotting attacks.

(Reporting by Nizam Ahmed; Editing by Sanjeev Miglani)

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