MEXICO CITY (Reuters) - President Felipe Calderon declared three days of mourning on Friday and demanded a crackdown on drugs in the United States after armed men torched a casino in northern Mexico, killing at least 52 people. Under intense pressure as violence soars, Calderon said he would send more federal security forces to the city of Monterrey, where gunmen set fire to an upmarket casino on Thursday in one of the worst attacks of Mexico's drugs war. Lashing out at corrupt officials in Mexico and "insatiable" US demand for drugs for fomenting the violence, Calderon urged the US Congress to stamp out drug consumption and stop illegal trafficking of weapons across the border into Mexico. "We're neighbours, we're allies, we're friends, but you are also responsible," a sombre and angry Calderon said to the United States in a speech after meeting his security advisers. Pledging to step up the fight on organized crime, Calderon said Mexico was under attack from "true terrorists", and told all Mexicans to come forward and denounce those responsible. "They aren't and cannot be the ones in charge of our streets, our cities and our future," he said Calderon first ordered a crackdown against the cartels when he took office in late 2006 and several senior traffickers have been arrested. However, turf wars between rival cartels have killed about 42,000 people, battering Mexico's reputation. The president insists his campaign has weakened the cartels but critics say it simply brought a surge in violence and has done little or nothing to slow the flow of cocaine, marijuana and other drugs into the United States. The carnage has hurt support for Calderon's conservative National Action Party (PAN), which already faces an uphill battle to retain the presidency in elections next July. The casino attack is particularly bitter for Calderon because the victims were mainly well-to-do civilians with no link to the conflict, in an area that has traditionally been a electoral stronghold for the business-friendly PAN. Monterrey, which lies about 230 km (140 miles) from the Texas border, is a relatively wealthy city of about 4 million people and is home to some of Mexico's biggest companies. It was for many years seen as a model of economic development but it has been ravaged by the drugs war over the past two years. The president was unrepentant on Friday and sought to pin blame for the violence on corrupt judges and politicians in "certain parts" of the country. It appeared to be an attack on the main opposition Institutional Revolutionary Party (PRI), which controls the majority of Mexico's states. With a big lead in opinion polls, the PRI is on track to oust the PAN from power next year and analysts expect the ruling party to intensify efforts to discredit its bitter rival as the presidential vote nears. Survivors from Thursday afternoon's attack said armed men burst into the Casino Royale and threatened gamblers before dousing gasoline on the carpets and setting it on fire. "My wife came here for a celebration," a weeping man told Milenio TV. "She was having dinner with her friends."