MITROVICA, Kosovo — For three months, this gritty mining town has been a hot spot of Balkan ethnic tension ominous enough to prompt new deployments of armed NATO peacekeepers and action by the European Union to slow Serbia’s long-sought bid for membership.

In the long siege at makeshift gravel barricades, ethnic Serbs hurled rocks toward ethnic Albanians on the other side of the Ibar River, and this summer, hooded men in shorts and sneakers firebombed a border-control station, stoking fears among Western powers that ethnic clashes could spin out of control in northern Kosovo.

As is often the case in this impoverished region, the truth is complicated. In this instance, the authorities say, a furious effort to protect a lucrative oil-smuggling operation has turned into an international episode stirring troubling memories of the Balkan ethnic carnage of the ’90s.

But with the trade estimated to run as high as $100 million annually, many observers say it has actually fostered a rare ethnic easing of tensions built around smuggling routes that run across divided territory.