Much of the political opposition in Kazakhstan, as in other Central Asian republics, is made up of politicians who were previous allies of the men in power but have fallen out with them and joined the opposition.

Altynbek Sarsenbaiuly became a critic of the Kazakh government

This is true of both the politicians who have recently died in Kazakhstan.

In November, in the run-up to the presidential election, Zamanbek Nurkadilov was found dead at his family home in Almaty with a revolver by his side.

President Nursultan Nazarbayev, who a few days later was duly re-elected to the office he had already held for 16 years, sent Nurkadilov's family a telegram of condolence, and an official enquiry concluded that it was a case of suicide.

But a lawyer for Mr Nurkadilov's family questioned whether it would have been possible for the former mayor of Almaty (and emergencies minister) to shoot himself twice in the chest before delivering a final shot into his head.

The opposition was quick to accuse Mr Nazarbayev of ordering the killing of Nurkadilov, who had been sacked after accusing the president of being involved in extensive corruption - the so-called "Kazakhgate" scandal - and other crimes.

Pro-government figures suggested, in response, that Mr Nurkadilov might have been killed by rival personalities within the opposition with whom he had a stormy relationship.

A critic silenced

The mysterious death of a second prominent Nazarbayev critic is bound to bring fresh accusations against the authorities.

Altynbek Sarsenbaiuly was co-chairman of the Nagyz Ak Zhol opposition party.

Previously he had served under President Nazarbayev, and was secretary of the national security council, information minister and ambassador to Russia before splitting with the presidential camp in 2003 and joining the opposition.

Kazakh President Nazarbayev has been in power for 16 years

His body was found riddled with bullets in his car, alongside his driver and bodyguard.

In the recent presidential campaign he had joined other opposition leaders in denouncing the election as fraudulent.

The affair will be regarded with concern by foreign partners of oil- and gas-rich Kazakhstan.

In the early years of independence, President Nursultan Nazarbayev was seen as a progressive and skilful leader, a reliable partner in developing his country's potential wealth.

But in recent years his rule has been dogged by controversy over restrictions on free speech and Mr Nazarbayev's controversial prolongation of his term in office, despite constitutional limitations.