The organisers of the bi-annual event have received complaints from several countries where Spanish embassies have allegedly blocked visa applications by those wanting to attend.

Many countries have endemic Aids infection

Medical experts, charities and campaigners are due to gather in the Spanish city from 7 and 12 July.

Delegates from the developing world who want to travel to the XIV International Aids Conference say they have been thwarted by Spanish bureaucracy.

In Uganda, there are reports that visa applicants have been asked to prove their HIV status to Spanish officials even though it is illegal to discriminate against HIV positive individuals under Spanish law.

In countries like India, Colombia and Nigeria, conference delegates say they have been unable to get the papers they need to travel from embassies because of the need to prove they are not planning to enter Spain to look for work.

Entry requirements

A spokesman for the Spanish foreign ministry denied that HIV positive delegates were banned from entering the country.

Let us hope that this is resolved or we will have to refrain from holding this type of conference in countries with such restrictive entrance policies

Shaun Mellors Conference community coordinator

However he confirmed that delegates would have to meet minimum economic conditions to enter Spain and would need to show they had medical insurance.

Shaun Mellors, community coordinator for the conference, said: "The international Aids conference is not held in the US because of this kind of problem.

"When Barcelona was chosen, we were guaranteed that participants would not have any problem.

"Let us hope that this is resolved or we will have to refrain from holding this type of conference in countries with such restrictive entrance policies."

"We do not understand this," said Joan Tallada of Red2002, a network of non-governmental Aids organisations participating in the conference.

In a statement, the conference organisers said: "The conference will do everything in its power and within the law to ensure that all registered delegates obtain the required permission to enter Spain."

It added: "The conference recognises that people from developing countries form an essential part of the conference programme.

"To this end, organisers have been in constant contact with the Ministry of the Exterior to expedite the visa process."

Delegates who have been refused visas to attend the conference have been asked to contact the organisers by email at jrubio@aids2002.com