Unidentified attackers have set fire to a kindergarten in the Mexican city of Ciudad Juarez, apparently after its owners refused to pay extortion money

A message was sprayed on the walls of the kindergarten urging the owners to pay up. The fire happened overnight, so no children were injured, the nursery has been closed down indefinitely. Ciudad Juarez is the most violent city in Mexico, with an average of eight murders a day. The nursery's owners had been approached by unidentified men who demanded an undisclosed sum in exchange for "protection", which was not paid, police told local media. Some teachers in the city have reported being threatened with attacks unless they hand over half their Christmas bonuses. Also armed men attacked two drug rehabilitation centers in the city killing four of the patients. Attacks on drug rehabilitation centers in Mexico are increasingly common. Police say the facilities are often used to recruit young men to work in the drugs trade, making them a target for rival drug gangs. Nine people were killed in an attack on a drug clinic in June 2010 in Durango state and 13 were shot dead in October 2010 in Tijuana, another city on the US-Mexico border. More than 30,000 people have been killed in drug-related violence over the past four years, since President Felipe Calderon declared war on the country's drug cartels.