By Zubair Ahmed BBC News, Mumbai

Smoking on screen is banned in India (Courtesy: Yashraj Films)

India's National Organisation for Tobacco Eradication (Note) threatened to sue the actor last week unless he replied to it within eight days.

The anti-smoking group said it was happy with Bachchan's apology.

The government banned tobacco adverts in 2003 and last year announced strict rules on smoking in films and on TV.

Hoardings

In the letter to the Goa-based anti-smoking group, the superstar promised not to step out of line in future.

"I have made a note of anti-tobacco legislation and have informed my producers and told them to take immediate steps so that no such violations take place," he said.

The publicity banner carrying my photograph is a still from the film depicting the underworld character of a don, which I'm portraying in the film Family Amitabh Bachchan

Note secretary Shekhar Salkar said he was satisfied with the reply.

"I am extremely happy. I was expecting nothing less from a person like Mr Bachchan," he told the BBC.

But Mr Salkar said he still intended to take legal action against the company which had put up the hoardings in Panaji, the capital of western Goa state.

He said he was making Bachchan a party to the case as well.

"Without him [Bachchan] my case does not stand, because he has broken the law."

Bachchan says the picture on the hoardings is a still taken from his latest film, Family, in which he plays an underworld figure.

The star is one of Bollywood's most recognised faces outside India, with more than 100 films to his credit.