Suspected Islamist extremists threw grenades and opened fire at Bangladesh officers, after militants were arrested in a major anti-extremist drive in the country's southeast, police said.
Four suspected militants, including a woman, from a group that has pledged allegiance to Islamic State were killed in a shootout on Thursday when Bangladesh police raided their hideout in the southeast, a senior police official said.
Police said those killed were members of a faction of the Jamaat-ul-Mujahideen Bangladesh group, known as New JMB, which they believe were linked to an attack on a cafe in the capital, Dhaka, last July that killed 22 people, most of them foreigners.
New JMB has pledged allegiance to the Islamic State militant group, which claimed responsibility for the attack on the cafe in Dhaka's diplomatic quarter, although the government has cast doubt on that claim.
Two policemen were wounded when the militants inside a two-storey building in Chittagong, about 200 km (120 miles) southeast of Dhaka, attacked them with at least a dozen grenades, police official Mohammad Moniruzzaman confirmed.
It was not clear whether the militants were killed in a shootout with police or had detonated suicide vests they were wearing, Moniruzzaman said.
"The operation is over. Our intelligence and bomb disposal units are now working," he said.
The raid on the building began on Wednesday night and 20 members of seven families trapped inside were taken to safety before the final assault began early on Thursday, Moniruzzaman said. Live bombs were found inside the building, he said.
Bangladesh has been hit by a spate of killings of liberals and members of religious minorities in the past few years.
Al Qaeda and Islamic State have made competing claims over the attacks in the mostly Muslim country of 160 million people, but the government has consistently denied the presence of any such transnational militant organisations in Bangladesh.
Authorities instead blame the violence on domestic militants, although security experts say the scale and sophistication of the cafe attack suggested links to a transnational network.
Police have killed more than 50 suspected militants in shootouts since the cafe attack, including the man they say was its main planner, Bangladesh-born Canadian citizen Tamim Ahmed Chowdhury.
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 "Bangladesh, Dhaka cafe attack, Mohammad Moniruzzaman, Chittagong, Jamaat-ul-Mujahideen, Islamic State, Tamim Ahmed Chowdhury,")
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