The Calais camp in northern France was shaken by a scandal as some unpaid charity workers were accused of sexually exploiting refugees and child migrants, the Independent reported on Thursday. Amid the allegations, the U.N. Refugee Agency (UNHRC) has urged charities in Calais to impose "zero tolerance" policies regarding relationships with refugees.Meanwhile, hundreds of migrants trying to make their way to the U.K. from Calais in northern France clashed with French riot police on Wednesday, Reuters witnesses and police said. Police used tear-gas grenades to disperse migrants trying to make their way to the access road for the Calais port. The clashes took place not far from where a British-financed wall is being built to seal off the road, where migrants frequently try to jump on trucks bound for the U.K.After weeks of preparation, workers have begun building a 4-meter (13-foot) high wall in northern France to try to keep migrants from sneaking onto ferries crossing the English Channel. Critics of the wall note that France plans to dismantle the makeshift camp by the time the wall is expected to be completed at the end of the year.The number of migrants living in the "jungle" reached as many as 10,000 this month according to aid groups operating in the camp, compared to 7,000 according to a tally by French authorities in August. There were a few hundred there in 2012 when French President François Hollande was elected.An 18-hectare wasteland in the French port city was turned into a camp in April 2015. Hundreds of migrants were relocated by French authorities where there is no access to basic services. Most migrants coming from the eastern African countries of Eritrea, Ethiopia and Sudan and war-torn Syria intend to cross the English Channel and seek asylum in the U.K. As only a small number of refugees are eligible to enter European countries,the ones that can find shelter suffer from worsening humanitarian conditions in refugee camps.