Facebook, the social networking site, has been accused of not keeping young users safe from sexual predators after an investigation revealed apparent defects in its safety controls.

The New York State attorney general has subpoenaed Facebook asking it to explain its security policy following an an undercover investigation in which authorities posing as teenagers received sexual advances within days of setting up profiles on the site.

In one instance, an investigator from the attorney general's office set up a profile for a 14-year-old girl who days later was contacted by a 24-year-old man asking for "nude pics."

When contacted about the message, Facebook said it would remove any post that violated its rules but a month later had still not taken any action.

The attorney general's office asked Facebook for documents relating to its security policy, as well as information about how it handles complaints from its 42 million users, according to the New York Times.

So far no charges against the company, which said it was taking the allegations "very seriously."

In a letter to Facebook's chief executive, the attorney general, Andrew Cuomo, said he was investigating whether Facebook's advertising was "materially misleading" under state laws that prohibit deceptive practices.

"'Facebook has the right to operate any type of Web site it deems fit,'' Mr Cuomo wrote. ''It does not have the right to represent that its site is safe and that it promptly responds to complaints when such statements are not accurate.''

The investigation follows calls from the 50 state attorneys general that social networking sites such Facebook and MySpace, which is owned by News Corporation, parent company of TimesOnline, improve safety measures for young users.

In July, MySpace said it removed the profiles of 29,000 convicted sex offenders from its database after cross-checking its members against offender registers.

As part of their investigation, officers at Mr Cuomo's office set up a profile for a 13-year-old girl, as well as one for an adult, who sent the teenager a message saying, "You've got quite a hot little bod."

When the investigator, posing as the girl's mother, forwarded the message to Facebook demanding that the company take action, there was no response.

The profile of the 24-year-old who asked for "nude pics" was still active a month after investigators - posing as the recipient - notified Facebook of his solicitations, Mr Cuomo said.

On its site, Facebook says it takes its users' safety "very seriously" and "quickly takes down any objectionable material that may be posted," in particular messages that "solicit personal information from anyone under 18."

In a statement yesterday, the company said: "'We take the concerns of the office of the New York attorney general very seriously."

The Child Exploitation and Online Protection (CEOP) Centre said today that it monitored all social networking sites for potential abuse by paedophiles, but did not single Facebook out as a cause for concern.

It said it was working with such sites to make children's safety "an utmost priority" and encouraged them to take responsibility for improving safeguards so that they were not "demonised" in the eyes of the public.

A Home Office spokeswoman said that new guidelines due out at the end of the year would force social networking sites to give users control over who can access their information, as well as make it easier for children to report problems or threatening behaviour they experience online.

"Social networking sites have exploded in recent years, and the Government wants to make sure that messages about how to use such sites safely continue to get through," she said.

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