DHAKA (AFP) - Suspected Islamists carried out another deadly attack in Bangladesh Thursday (July 7) at the country's biggest prayer service for the start of Eid, days after a mass murder of hostages in the capital Dhaka.

Authorities said four people, including two policemen, had been killed after several explosions and gunfire near a prayer ground in Kishoreganj district as at least 250,000 people joined a post-Ramadan gathering.

"Two policemen, an attacker and a woman who was shot during the gunfight were killed," national police spokesman A.K.M. Shahidur Rahman told AFP.

"Nine policemen were also injured. They are in a critical condition and have been shifted to a military hospital in Dhaka." Another senior officer said that a group of at least three attackers had hurled hand bombs at police manning a checkpoint just outside the main prayer ground, which is around 150km north of Dhaka.

Nearly 1,000 police were on duty in Kishoreganj at the time of the attack.

"We responded with gunfire. A gunfight ensued and they fired back and threw more hand bombs," Tofazzal Hosain, the northern district's deputy police chief, told AFP.

Two attackers were arrested, including one who had been shot and injured, while a pistol and machete were recovered from the scene.

The gathering in Kishoreganj is known as the Sholakia Eid prayers and officials put the number of people at the service on Thursday at between 250-300,000.

It is by far the biggest such congregation in Bangladesh, a mainly Muslim country that is home to around 160 million people.

While there was no immediate claim of responsibility, it came less than a week after Islamists killed 20 hostages and two policemen in an overnight siege at a Western-style cafe in Dhaka. All the victims, including 18 foreigners, were hacked to death with machetes.

Bangladesh has been on a heightened state of alert in the wake of the killings in Dhaka last Friday night and many Eid services included pleas from religious leaders for an end to the violence.

"Allah, protect our country ... and protect our children from the evils of terrorism," Mohammad Sadequl Islam, the local imam, told a gathering of around 5,000 devotees at Dhaka's Mahakhali neighbourhood.

Many of those who attended services in Dhaka could be seen weeping as clerics led prayers for a more peaceful and prosperous Bangladesh.

The biggest service in the capital was at the National Eidgah Maidan where more than 50,000 people, including Bangladesh's President Abdul Hamid, took part in prayers under a giant canopy.

Police brought in scanners and sniffer dogs to check for bombs as crowds were forced to wait for up to an hour before being cleared to enter the grounds where the service was held. No one was allowed to bring in bags.

Bangladesh has been reeling from a growing wave of attacks since the turn of the year, many of which have been claimed by the self-styled Islamic State in Iraq and Syria (ISIS) group or an offshoot of the Al-Qaeda network.

However Prime Minister Sheikh Hasina's government has consistently denied international terrorist networks have gained a foothold and have said the weekend attack in Dhaka was carried out by a local Islamist group.

Bangladesh's Information Minister Hasanul Haq Inu again portrayed the latest attack as being designed to topple Hasina.

"We don't know which group they belong to but they are suspected members of extremist terrorist group. They are against the normal religious practices of the country," he told AFP.

"They are anti-Islam, anti-religion and anti-government. They have a political as well as a religious agenda."

Critics have said Hasina's administration is in in denial about the nature of the threat posed by extremists and accuse her of trying to exploit the attacks to demonise her domestic political opponents.

Last month authorities launched a crackdown on local militants, arresting more than 11,000 people but critics allege the arrests were arbitrary or designed to silence political opponents.

Bangladesh's main Islamist party has been banned from contesting polls and most of its leaders have been arrested or else executed after recent trials over their role in the 1971 war of independence from Pakistan.