The protests threatened to derail the EU leaders' summit after around 7,000 farmers surrounded EU institutions in Brussels to oppose the Mercosur trade deal, following an earlier mobilisation that brought tractors and thousands of demonstrators into the city centre.Organisers said nearly 8,000 people and more than 500 tractors from about 40 farming groups across the EU joined actions that blocked roads, disrupted public transport and led to clashes in which police used tear gas, water cannon and pepper spray.Reporters cited videos and photographs showing scuffles, burning tyres, fireworks and at least one window smashed at Station Europe as authorities warned of delays and possible disruption to summit talks.