The United Nations has renewed its warnings to Uruguay and the US states of Colorado and Washington that their cannabis legalisation policies fail to comply with international drug treaties.

The annual report from the UN’s International Narcotics Control Board, which is responsible for policing the drug treaties, said it would send a high-level mission to Uruguay, which became the first country to legalise the production, distribution, sale and consumption of cannabis for recreational purposes.

The UN drug experts said they would also continue their dialogue with the US government over the commercial sale and distribution of cannabis in Colorado and Washington state.

The possession and cultivation of cannabis became legal on 26 February in Washington DC. Voters in Oregon and Alaska have also approved initiatives to legalise the commercial trade in cannabis for non-medicinal purposes.

The INCB said it “continues to engage in a constructive dialogue” with the US government on cannabis developments and it is clear the UN is putting strong pressure on the US government to ensure that the drug remains illegal at a federal level.

The US government has issued new guidance to banks on their provision of services to marijuana-related businesses and all state attorneys have been reminded of the need to investigate and prosecute cannabis cases in all states.

The INCB said it was aware that the US government intended to monitor the impact on public health of legalising cannabis and has again reminded the Obama administration that the position in Colorado and Washington meant the states were failing to comply with the treaties.

Lochan Naidoo, the INCB president, said the limitation of use of narcotic drugs and psychotropic substances to medical and scientific purposes was one of the fundamental principles underpinning the international drug control framework. “This legal obligation is absolute and leaves no room for interpretation,” he said.

The UN body also renewed its call for the abolition of the death penalty for drug-related offences and voiced concern that Oman was proposing to make use of the death penalty for drug-trafficking offences.

The INCB’s annual report records a further rise in the number of new “legal highs” or psychoactive substances that have been identified. The number has risen from 348 to 388 in the past year – an increase of more than 11%. More than 100 countries are taking action against “legal highs” and the INCB has welcomed moves by China, considered by many to be one of the main sources, to start banning these synthetic substances that imitate the effects of traditional drugs such as cannabis and ecstasy.

The UN drug board also warns of a 66% increase in the global consumption of a stimulant, methylphenidate, which is primarily used in the treatment of ADHD or attention deficit hyperactivity disorder and is better known by one of its trade names, Ritalin. The rise has been seen in its use by teenagers and young adults in the US, Iceland, Norway, Sweden and Australia.

It also highlights the lack of access for 5.5 billion people to medicines containing drugs such as codeine and morphine, which means that 75% of the world’s population do not have access to proper pain-relief treatment.