Paris - Vehicle attacks of the sort seen in Barcelona are easy to organise and difficult to stop and have become part of a new reality for Europeans, experts say.Paris, Berlin, Nice, London and Stockholm have already seen extremists drive vehicles into crowds. The latest attacks in Barcelona and the seaside resort of Cambrils left at least 14 dead and 100 injured on Thursday night.The atrocities by extremists willing to die carrying out an attack are likely to lead to a rash of new security measures designed to protect pedestrians. But experts warn that citizens' safety cannot be guaranteed 100 percent."It's the principle of 'soft targets'," Frederic Gallois, the former head of France's elite GIGN police force, told AFP. "Any gathering of people is a soft target and there are crowds everywhere."Even if security services managed to protect symbolic sites and the most popular areas around cities, nearby streets or neighbourhoods would still be vulnerable, he said.The unsophisticated low-cost attacks are in sharp contrast to the highly coordinated and planned assault on Paris in November 2015 which left 130 dead. But they are very much part of the strategy of terror groups such as Al-Qaeda and the Islamic State group (IS).Both extremist groups have urged their followers to use whatever means at their disposal, including vehicles, as part of a strategy of "death by a thousand cuts" aimed at destroying the West."They aren't looking for spectacular results using huge resources, but rather they want frequency to try to destabilise their adversaries," Gallois added. "It's the regularity which is the problem."At the moment, there's an attack every four to six weeks in Europe," he added. Then with each lull, "everyone says to themselves 'something's going to happen'."- Learning to live with terror? -Many countries have increased the number of armed security forces patrolling Europe's streets to deal with the threat, while police are now well-drilled in responding to incidents.Further investments in intelligence-gathering and information-sharing between EU members could also help reduce the risk of future violence, some experts believe.In Syria and Iraq, military action by Western powers and their local allies has also shrunk the territory and resources available to IS, which claimed Thursday's attack in Barcelona.Jean-Pierre Filiu, an expert on terrorism at the Sciences Po university in Paris, warned against thinking the military defeat of the organisation would bring an end to the wave of assaults."They want to show that they are still effective despite the territorial losses. But it's not because they are retreating in Iraq and Syria that they are striking now," he said on France Inter radio. The Radicalization Awareness Network, an EU research body, warned last month that 1,200-3,000 jihadists risked returning to Europe after fighting in Iraq and Syria -- out of an estimated 5,000 who joined the terror groups there.Nathalie Goulet, a French senator who sits on a parliamentary panel tasked with analysing jihadist groups, said it was important to avoid anti-Muslim rhetoric, which plays into the hands of the extremists.One of IS's stated goals is turning Western governments and citizens against Muslim minorities in their countries."You need to look at the reality. Telling people that banning Muslims... or closing mosques will resolve the problem is lying," she told AFP in a recent interview."Someone who gets into their car and crashes into a crowd, unfortunately we need to learn to live with that and every citizen must remain vigilant," she said.