The International Narcotics Control Board (INCB) also said Honduras, Costa Rica and Nicaragua had become major transit countries for traffickers.

North America remained the biggest drugs market, the INCB's report said.

The board also warned that illegal internet pharmacies are increasingly using social media to target consumers.

Drug-related violence in Central America involving trafficking organisations, local and transnational gangs, and other criminal groups "has reached alarming and unprecedented levels", the INCB's annual report says.

The report notes that El Salvador, Guatemala and Honduras, together with Jamaica, now have the world's highest murder rates.

Central America is home to some 900 "maras", or streets gangs, which have 70,000 members.

This combined with the widespread availability of guns has contributed to high levels of crime, the INCB says.

In 2010, Honduras together with Costa Rica and Nicaragua, which both have significantly lower levels of crime, became major transit countries for drug smuggling gangs, the INCB said.

The US, Canada and Mexico remain the biggest market for drugs, with all three countries continuing to have "high levels of illicit drug production, manufacture, trade and consumption".

The INCB also expressed concern at steps taken by Bolivia to seek to legalise the chewing of coca leaf.

The practice went against international drug conventions, the Vienna-based INCB said.

Bolivia wants to amend the 1961 UN Single Convention on Narcotics Drugs to remove language that bans the chewing of coca leaf.

The Bolivian government argues that it is discriminatory, given that coca use is so deeply rooted in the indigenous culture of the Andes.

Elsewhere in its report, the INCB notes that illegal internet pharmacies are turning to social networking sites to publicise their websites and so apparently targeting a young audience.

This is particularly dangerous as the World Health Organization has found that more than half of medicines from such sites are counterfeit, the INCB says.

There were 12,000 seizures of internationally controlled substances sent through the post in 2010.

India was the country of origin for more than half the seizures, while significant amounts also came from the US, China and Poland.