HANBE - A previously unknown Islamist group claimed responsibility on Wednesday for a deadly suicide car bombing in Tajikistan last month that killed two police officers.

A shadowy group calling itself Jamaat Ansarullah said it had carried out the bombing in the northern city of Khujand as revenge for attacks against Muslims, in a letter posted on the kavkazcenter.com website.

"The operation was conducted in response to the killing and humiliation of our brothers and ordinary Muslims which have taken place outside of this God damned place," the letter said.

"As a result of the operation, according to our preliminary data, at least 50 apostates have been killed or wounded."

Kavkazcenter.com, a pro-militant website which often acts as a mouthpiece for statements by Islamist groups in the region, said it received the claim of responsibility in an unsolicited email.

It was not possible to immediately verify the claim.

Late last month a pair of suicide bombers rammed an explosives-packed car into a police station in Tajikistan's second city of Khujand, killing two and wounding at least 25.

That blast came after Tajikistan President Emomali Rakhmon sacked his long-time security boss following a humiliating prison break in which a group of 25 Al-Qaeda-linked militants escaped and killed six guards.

Police in Tajikistan, the poorest country to emerge from the collapse of the Soviet Union nearly two decades ago, had blamed both attacks on militants from the Islamic Movement of Uzbekistan.

A bombing at a nightclub on the outskirts of the capital Dushanbe this week has further heightened tensions and led to speculation that violence from neighbouring Afghanistan could be spilling across the border.

Tajikistan, where a civil war between Islamist forces and backers of Rakhmon's secular government killed tens of thousands following the collapse of the Soviet Union, shares a porous 1,300-kilometre (800-mile) border with Afghanistan.