A global human rights group on Friday urged Bangladesh to order an independent investigation into the growing number of cases where opposition members and activists have disappeared.

The New York-based Human Rights Watch expressed concern as local rights group Ain-O-Salish Kendra said at least 22 people have disappeared this year. Another Dhaka-based group, Odhikar, says more than 50 people have disappeared since 2010.

Security agencies including the elite anti-crime force Rapid Action Battalion have been blamed for many disappearances, but the agencies deny the allegations.

Bangladesh's opposition parties enforced three days of nationwide general strike this week to protest the latest disappearance: that of opposition official Elias Ali, who went missing April 17, along with his driver.

Ali's car was recovered later after residents found it abandoned on a street in the capital, Dhaka.

The main Bangladesh Nationalist Party led by former Prime Minister Khaleda Zia has given the government of Prime Minister Sheikh Hasina a Saturday deadline to find Ali, otherwise, it would enforce "tougher" anti-government protests.

The opposition party and its 17 other allies have blamed the government and security agencies for Ali's disappearance, but the government rejected the allegation and sought the opposition's cooperation to find him.

"The rise in disappearances, particularly of opposition members and activists, requires a credible and independent investigation," said Brad Adams, Asia director at Human Rights Watch.

"The government has taken no serious steps to ensure such an investigation of these disappearances nor to prevent them in the first place," he said.

Human Rights Watch said it has long documented abductions and killings by Bangladeshi security forces, especially by the Rapid Action Battalion, which has earned praise because of its fight against some radical Islamic groups in recent years.

In an annual report, Human Rights Watch this year noted that although the number of killings by the battalion had dropped following domestic and international criticism, there had been a sharp increase in enforced disappearances, with persons disappearing after last being seen in the custody of security agencies.

It said such cases are triggering concerns that security agencies have replaced one form of abuse with another. But Bangladeshi authorities routinely refuse to confirm the detention or fate of those persons who disappear after being seen in their custody, it said.

The group criticized the government for its alleged failure in ensuring justice for the victims.

The South Asian nation's opposition parties have also accused police of using excessive force to tame recent anti-government protests. But the government said tight security was needed to protect the innocent people as the opposition protests, which it says were designed to create anarchy in the country.