Three suspected Islamist extremists were killed in a raid by Bangladesh police just days before the Pope is due to arrive in the country.

The suspects opened fire and threw bombs at Rapid Action Battalion police who cordoned off a house where they were hiding near the border with India, officials said.

"We called on them to surrender. But they responded by opening fire and throwing bombs. Moments later we heard loud explosions inside the house," Major Ashraf, an RAB officer, told AFP.

The officer said a search of the tin-roofed house in Chapai Nawabganj district in the northwest of the country was being completed.

RAB deputy head Colonel Anwar Latif Khan told AFP that "three people who were involved in Islamist militancy were killed" in the explosions.

RAB officials said the house was raided following a tip-off.

Pope Francis arrives in Bangladesh on Thursday for a three-day visit, the first by a Vatican leader in 31 years.

The visit will be dominated by the plight of more than 620,000 Rohingya Muslims who have fled ethnic unrest in Myanmar and taken refuge in Bangladesh.