President Aliyev is still undergoing treatment in the US

A statement by Mr Aliyev read on Azeri television said that he was withdrawing from the election in favour of his son, Ilham, who is also a candidate.

The 80-year-old president has been in hospital in the United States for more than two months, receiving treatment for heart and kidney problems.

He has not appeared in public since he entered a Turkish hospital in mid-July.

Unfortunately, the state of my health does not allow me to realise my plans - I declare that I am withdrawing my name in favour of Ilham Aliyev Heydar Aliyev

Mr Aliyev, a former KGB chief who has run the republic on and off for more than 30 years, appointed his son prime minister on 4 August.

Speculation that he would try to pass the presidency on to his son has been rife since he collapsed during a televised speech in April.

In the message, which was read out on state TV, Mr Aliyev said he thought he would soon recover and come home, but that he could not continue as president.

Groomed

Ilham Aliyev has a reputation as a playboy

"Unfortunately, the state of my health does not allow me to realise my plans," he said.

"I declare that I am withdrawing my name in favour of Ilham Aliyev. He is my political successor.

"I trust him as I trust myself and pin great hopes on him in what concerns the future of Azerbaijan."

The BBC's Chloe Arnold in Baku says Ilham Aliyev has a reputation as a playboy and a gambler.

In recent years he has been groomed for leadership, but many analysts doubt that he has the ruthlessness or the appetite for power required to fill his father's shoes.

Some predict he will take on the role of an interim leader, ensuring a smooth and peaceful transition from his father's rule - and then handing over power to someone else.

"It is very easy for Ilham to come to power, but it will be hard for him to hang on to power," said Elmar Husseinov, a political analyst.