(Adds case filed against ex-minister, background)

DHAKA, March 31 (Reuters) - Bangladesh police busted a den of suspected militants in the capital hours after six Islamists were hanged on Friday for a series of bomb attacks in 2005.

The army-backed interim government has vowed to stamp out extremist violence and security has been beefed up across the country, which has been under emergency rule since January.

Police said they had detained 22 suspected militants meeting in Dhaka's Mohammadpur area.

They said the detainees were members of Hizbut Tahrir, an Islamist group, and were being interrogated.

Police also captured two suspected members of the Jamaat-ul-Mujahideen group in northern Rajshahi district on Friday.

Police said among those hanged were Bangla Bhai, chief of the outlawed Jagrata Muslim Janata Bangladesh group, and Shayek Abdur Rahman, supreme leader of Jamaat-ul-Mujahideen.

Authorities, fearing reprisals, tightened security across the country on Saturday. Police and the elite Rapid Action Battalion searched vehicles and pedestrians, witnesses said.

The government has vowed to continue the hunt for Islamists, alongside a drive against corrupt politicians.

Police said they had opened a probe against a former minister in the then government of prime minister Begum Khaleda Zia for abetting Islamists.

"A case has been filed on Saturday against Aminul Haque, former telecommunications minister, for abetting Islamists who tortured a farmer in 2004," said Inspector Golam Sarwar in Rajshahi.

Farmer Fazlur Rahman, who was maimed and was evicted from his land by supporters of Bangla Bhai, charged that Haque had repeatedly ignored his complaints against the Islamists.

Haque went into hiding after police launched a drive against corruption after the imposition of a state of emergency on Jan. 11 following widespread political violence. An election planned for Jan. 22 was postponed.

Police have arrested more than 160 key political figures, including Tareque Rahman, eldest son of Khaleda and a senior joint secretary of her Bangladesh Nationalist Party.

(Additional reporting by S.M. Humayun Kabir in Rajshahi)

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