By Andrew Walker BBC Economics Correspondent

A meeting of trade officials in Geneva has again failed to resolve rules affecting poor countries' access to cheap medicines.

The discussions in the World Trade Organisation (WTO) were about the circumstances in which countries can override patents to import medicines needed to deal with serious public health problems.

The talks have already failed to meet a self-imposed deadline of the start of this year.

The problem relates to poor countries with serious public health problems such as HIV/Aids, which could be tackled with drugs that are covered by patents

More than a year ago, the WTO agreed that developing countries should be able to make cheap copies.

But they could not decide what to do about countries that do not have the industries to manufacture drugs themselves.

The conclusion will almost certainly be a system that allows them to import cheap copies from other countries.

Sticking point

But agreement has been held up by concerns among patent holding companies that the whole system of patent protection might be undermined - a worry that United States negotiators especially have taken up.

They wanted a list of diseases covered, whereas developing countries wanted the freedom to decide for themselves.

A trade official said the list issue is probably soluble.

But now it appears that some patent holding companies are concerned that countries that can make the necessary medicines drugs might instead choose to import them from others.

It is not clear why they are worried - but it is very clear that the WTO member countries want this issue settled soon.