About one-third of under 18s can buy cigarettes in a shop or pub, a watchdog has revealed.

The Office of Tobacco Control (OTC) said it was unacceptable for children to be sold cigarettes but said shopkeepers were now complying with the law more than ever.

The Irish Cancer Society said the report showed a ban on in-store displays and branding was protecting youngsters' health.

Kathleen O'Meara, the charity's head of advocacy, said figures show more than half of all smokers start before the age of 15, and 83% start before 18.

"These anti-tobacco measures are the next step after the workplace ban and are necessary to protect young people from the marketing tactics of tobacco companies who use shops and displays to attract young smokers," she said.

The Irish Cancer Society said lung cancer is the biggest cancer killer with 1,700 people dying every year while 6,000 people die from the effects of tobacco in Ireland.

"More than 90% of lung cancer deaths are preventable because they are caused by smoking," Ms O'Meara said. "Lung cancer is on the rise, particularly among young women and measures like the Point of Sale legislation are vitally important to protect children from being targeted and becoming addicted to cigarettes."

The OTC audit found the amount of retailers refusing to sell cigarettes to under 18s has increased to 68% - compared to 60% last year and 52% in 2007.

It also found compliance with laws on sales to children from vending machines in bars, pubs and clubs has also increased, with 65% refusing to sell cigarettes to minors, up from 37% last year.

Aine Brady, junior health minister, said: "Retailers and those in charge of licensed premises must take responsibility and ask all young people for proof of age ID."