The U.N.'s disarmament chief warned Wednesday that terrorists and non-state actors are using the so-called dark web to seek the tools to make and deliver weapons of mass destruction. "The global reach and anonymity of the dark web provides non-state actors with new marketplaces to acquire dual-use equipment and materials," U.N. High Representative for Disarmament Affairs Izumi Nakamitsu told a meeting of the U.N. Security Council. The dark web is a part of the internet that requires special software to access and allows users and website operators to remain anonymous or untraceable, making it appealing to criminals, terrorists and pedophiles. Nakamitsu said that dual-use items are complicating their efforts to address the risks posed by WMD. "We must keep in mind that many of the technologies, goods and raw materials required for developing weapons of mass destruction and their means of delivery derive from legitimate commercial applications that benefit many people," she said. Nakamitsu added that it is important to strike the right balance between collective security and commercial opportunity with preventing proliferation. Weapons of mass destruction include nuclear, chemical, radiological and biological weapons. "While there are still significant technical hurdles that terrorist groups need to overcome to effectively use weapons of mass destruction, a growing number of emerging technologies could make this barrier easier to cross," Nakamitsu said. In addition to the dark web, she said the use of drones and 3-D printers by non-state actors are also growing concerns. Nakamitsu urged intensified international cooperation to make it harder for terrorists and criminals to illegally traffic sensitive materials. Chemical weapons Terrorists have already used poison gas in at least one deadly attack. In Syria, Islamic State used mustard gas on civilians in the town of Marea in August 2015, according to a U.N.-authorized investigation last year. (The same investigators also concluded that the Syrian government carried out at least two chemical weapons attacks on civilians living in rebel-controlled areas in 2014 and 2015.) "The use by non-state actors of chemical weapons is no longer a threat, but a chilling reality," Joseph Ballard, a senior official with the Organization for the Prohibition of Chemical Weapons (OPCW) told council members. Ballard said the OPCW is working to enhance the security of the global supply chain of dual-use materials and technologies, including working with international customs officials. He said the organization also works closely with the international chemical industry, to ensure that toxic chemicals do not fall into the wrong hands.