A Bangladesh court has sentenced two prominent human rights activists to two years in jail, in what critics say is part of a crackdown ahead of elections.

Adilur Rahman Khan and Nasiruddin Elan from rights group Odhikar always denied decade-old charges that they published a report with false information.

But prosecutors said their report on security force killings in 2013 "undermined" the country's image.

The two were convicted on Thursday in Dhaka after a 10-year judicial process.

Dozens of international human rights groups have called for the two men's immediate release, saying the pair were denied a fair trial.

Both activists have spent decades documenting thousands of alleged extrajudicial killings, disappearances of opposition activists and police brutalities in Bangladesh.

They were convicted for a report Odhikar published in 2013 about a protest by an Islamist group which had sought to impose a stricter form of the religion on Bangladeshi society.

Their report documented that security forces killed at least 61 people, including children, in an overnight operation in Dhaka to remove protesters.

Khan and Elan were detained shortly after the report was published and then released on bail. The charges were only again picked up by prosecutors in recent times.

"They were sentenced to two years in jail for publishing and circulating false information, hurting religious sentiments and undermining the image of the state," prosecutor Nazrul Islam Shamim told the AFP news agency.

Human Rights Watch has pointed out prosecutorial action on their case did not proceed until 2021- after US sanctions were brought against Bangladesh's elite paramilitary force for their alleged involvement in hundreds of enforced disappearances and extrajudicial killings since 2009.

Last week, the United Nations also highlighted that both men had faced harassment and intimidation while on bail.

Rights groups have called for the two men's immediate release, saying their trial had been marred with "due process violations", such as a failure to provide the defence with crucial information until a day before the hearing.

"In addition to targeting Odhikar's leaders, the Government interfered with the organization's ability to conduct its human rights work by blocking their access to funds and leaving its registration renewal application pending since 2014," read a statement signed by 39 international rights groups.

Sheikh Hasina's government has been accused of targeting activists and political opponents since she became leader of Bangladesh in 2009 - something she denies.

Last year, the government cancelled Odhikar's operating licence, accusing it of tarnishing the country's image.

Under Khan's and Elan's leadership, Odhikar had worked closely with the UN and international human rights groups. Its reports were also cited in US State Department country reports.

The jailing of the activists comes just four months before Bangladesh's next general election and amid growing calls to ensure free and fair polls.