Anyone who takes part in a long-distance run knows there will be plenty of problems to overcome, but the Gaza marathon was always going to be in an endurance class of its own. When I registered for this year's race, my concerns were certainly less about my personal training schedule than about global conflict. The length of the blighted Palestinian territory is slightly shorter than the 26 miles and 385 yards required for an official marathon course, making its densely packed population particularly vulnerable to military action by its neighbour Israel. Destroyed buildings and potholed streets dot the entire route as it snakes along the Mediterranean coast, marking it out as the most dangerous in the world.

It was this aspect of runner risk – one that transcends the usual worries such as dehydration, pulled muscles and sunburn – that was the principal motivation for foreigners such as me. Through spending a few agonising hours with the ordinary people of Gaza on their war-ravaged roads, we would not only be able to empathise with their despair, but publicise it to the world outside. Hopeful idealism is easily manipulated, especially in the often cynically corporate realm of international sport, but in this case everybody's motives for entering appeared to be particularly meaningful.

This is why the 807 runners preparing for this year's marathon – the third to be organised by the United Nations' refugee agency Unrwa – were astonished, not so much by the fact of its sudden cancellation, but by the reason for it. Rather than the threat of violence from a neighbour in a position of overwhelming military superiority being the cause, the increasingly high-profile run was deemed too liberal by Hamas, the Islamic resistance movement that has governed the Gaza Strip since 2007, leading them to ban women from taking part. The UN organisation cancelled the race as a result.

Ultra-conservative Hamas leaders do not want to see women running alongside men, as they have done for the past two years, along with 1,600 Palestinian children, both boys and girls, who completed the course in relays.

Hamas's decision to ban women – 119 from abroad and 266 from Gaza itself – is wrong for all the most basic reasons. It is sexist, discriminatory and regressive, and – crucially – it wastes what should have been yet another huge blow against Israel's illegal occupation and blockade of the Palestinian territories. What the ban ultimately shows is that the Palestinian Authority, Hamas's more liberal political opponent based in Ramallah, is increasingly losing influence. War and occupation inevitably lead to authoritarian government, and Hamas is asserting its traditional conservatism in a manner that is of great concern to thousands of Palestinians.

Hamas insists that it merely wants "local customs respected", but women keeping most of their bodies covered as they ran was apparently not enough. The movement has absolute power in Gaza, and objected to an entire community uniting with foreign supporters in a show of solidarity. The fact that money from the marathon would be spent on supporting summer camps for Palestinian children appeared of little concern to Hamas.

This shortsighted ban comes as Israel introduces segregated buses travelling from the West Bank into Israel. The claim is that the buses will be popular with Palestinian workers, but they in fact come in response to demands from Israeli settlers who see these labourers as a "security threat". It is all part of a colonial expansion that currently sees Israelis building new homes on Palestinian lands in the West Bank and East Jerusalem, while Israel maintains control of Gaza's land and sea borders, its territorial waters, its natural resources, its airspace, its food and energy supplies, and its telecommunications network. All of this prompted David Cameron to call the Gaza Strip a "prison camp". Israel had no control whatsoever over the marathon, which was due to take place on 10 April, and the race was certain to draw attention to what is arguably the most pressing political problem in the Middle East, if not the world, today. Through rejecting a chance to highlight it because of petty objections to women going for a run, Hamas has made a serious mistake.

• This article was amended on 6 March 2013. One sentence originally read "It is sexist, discriminatory and regressive, but – crucially – it wastes what should have been yet another huge blow against Israel's illegal occupation and blockade of the Palestinian territories". The author meant "and" rather than "but", and we have now changed this word at her request.