Spanish police unions have sounded the alarm over the rise of drug cartels in the Bay of Gibraltar after nine officers came under attack from a group of 40 people attending a communion at the weekend.

The elite unit of Guardia Civil, who were off duty, were leaving a restaurant in Algeciras on Saturday afternoon when they were assaulted by the crowd, armed with baseball bats, stones and broken bottles. The police were forced to fire warning shots in the air to escape their assailants, who had been celebrating a communion at a nearby bar.

A spokesperson for the Guardia Civil said the attack was believed to be a “reprisal” for the fight against drug trafficking in the area, which saw cocaine seizures rise by 300 percent last year.

Alberto Moya, secretary general of the Unified Association of Guardia Civil (AUGC), an umbrella union, said there was a “grave risk” of drug cartels implanting themselves in the region. The criminal groups that had traditionally smuggled cannabis and tobacco in the Bay of Gibraltar were now “organizing themselves hierarchically to structure the business” and had “legions of youth in their pay” in the impoverished area, he told Spanish radio station Cope on Monday.