Whenever there is a humanitarian crisis, the international aid organisation, Médecins Sans Frontières (MSF), needs to find the resources to provide emergency care for those in need. Currently the organisation is active in more than 60 countries around the world and its resources are stretched, so you would think that MSF's Jewish UK executive director, Marc DuBois, would be lobbying the government to provide more assistance in these countries. However the Philadelphia-born aid worker has found himself in the unusual position of opposing government-sponsored medical aid.

The organisation was forced to withdraw from Afghanistan in 2004 when four of its staff were murdered. It has recently moved back into the country, but DuBois is concerned that the UK government has announced a policy linking humanitarian aid to its foreign policy aims. He says: "In Afghanistan, the military's provincial reconstruction teams have been building healthcare facilities. It sounds almost absurd for a medical aid organisation to be opposed to that. But what we see are the consequences - that the aid becomes politicised and the healthcare becomes compromised. People on the ground are afraid to attend those facilities because they are scared that if they do it might be seen as collaborating with the enemy. When the delivery of healthcare is placed in the service of military and political objectives, it makes it harder for us to treat a sick child."

DuBois is also worried that his workers and those in most need of medical care may become targets if they are wrongly identified as having links with a belligerent party. "We have to be trusted. Our neutrality and our independence should be an effective shield for us. We should be able to drive out there in the middle of a battle and not have people shooting at us. But this does not always happen. Everyone uses white vehicles. At times we painted our Landcruisers pink just to distinguish them."

It is not only in Afghanistan that MSF has to walk a political tightrope in order to deliver aid. It is a pressing issue in Gaza and the West Bank, too. And to maintain its emergency services for the needy, it has to maintain a dialogue with all parties. "We don't distinguish between good actors and bad actors. We negotiate with Hamas, Fatah, the Israeli Defence Force and the Jordanians, just so that we can treat people in need."

DuBois acknowledges that it would be politically complicated if for some reason MSF had to respond to an emergency in Israel. "I don't think that would happen because Israel has a world-class healthcare system. Having said that, the whole point about humanitarian aid is to be able to respond to a human in distress. It shouldn't matter if they are Jewish or Arab or if they have political beliefs with which you disagree. We responded in Rwanda to genocide against the Tutsis and then when the situation changed, we were in the camps treating the Hutus."

So, on what grounds does MSF decide to become involved? DuBois ponders: "There's no precise formula. What you look for is a population in crisis. There are needs everywhere but a crisis is something different. Haiti is the classic example of a nation in crisis without a proper healthcare system.

"Our niche is to some extent to put a Band-Aid on things. It sounds terrible but if your child has malaria, you don't need the whole situation fixed, you need treatment for your child."

DuBois, who read philosophy at Yale before joining the US Peace Corps to work in the African state of Burkina Faso, became fascinated by the advocacy side of international aid. After working for four years in a law centre in New Orleans, he joined MSF in 1999, with a particular interest in bearing witness to the suffering of people in danger. This is where MSF's policies are different from those of, for example, the International Red Cross, which practises a quieter, more discreet type of diplomacy.

But DuBois insists that MSF is political only when it needs to be. "We take a position only when a situation is unacceptable - where we are witnessing a mass violation of human rights. Then it is our duty to speak out."