Terrorist incidents, including deadly attacks, continued to plague Europe in 2013. Some attacks were apparently perpetrated by "lone offender" assailants while others were organized by groups claiming a range of extremist ideological motivations, from nationalism to right-wing and left-wing political theories to various religious beliefs, including violent Islamist extremism. In some cases the boundaries between ideologies were blurred.
A major challenge to Europe was the increasing travel of European citizens – mostly young men – to and from Syria seeking to join forces opposing the Asad regime. Many of them ended up in the ranks of violent extremist groups such as al-Nusrah Front or the Islamic State of Iraq and the Levant (ISIL). These "foreign fighters" sparked increasing concerns, and actions to address them, by European countries worried about the growing number of their citizens traveling to the battlefield and possibly returning radicalized. European governments, in particular the EU and several member states affected by this phenomenon, took action to assess the problem and to devise an array of responses to discourage their citizens from going to Syria to take part in the conflict. These efforts ranged from new administrative procedures to prevent travel to Syria, to steps to counter recruitment and facilitation efforts, and programs to investigate and/or reintegrate persons returning from conflict zones. In the western Balkans, governments in EU candidate states and aspirants were also committed to responding effectively to the foreign fighter problem, and sought assistance to fill gaps in their capacity to do so from the United States, the EU, and others. European governments also worked with the United States and other international partners in various fora, including the Global Counterterrorism Forum, to respond to the foreign fighter problem and strengthen general counterterrorism cooperation.
The Bulgarian government continued its investigation of the July 2012 attack in Burgas which left five Israelis and one Bulgarian citizen dead. In February 2013, the government publicly implicated Hizballah in the bombing. A court in Cyprus convicted a Lebanese Hizballah operative of various criminal offenses after he was apprehended surveilling potential Israeli targets on the island. Recognizing the threat posed by Hizballah, the EU in July 2013 agreed to designate what it termed the "military wing" of Hizballah as a terrorist group, a notable step forward.
Europe was the scene of several significant terrorist attacks in 2013. In Turkey, the most significant such incident in the country's modern history took place in May when 52 people died in a bombing in Reyhanli, on the border with Syria. In the Russian city of Volgograd, an attack on a city bus in October and two more attacks at the end of December claimed a total of 41 lives. The U.S. Embassy in Ankara was the target of a suicide bomb attack by a member of the Revolutionary Liberation People's Party/Front in February, in which a Turkish citizen on the Embassy guard force was killed. In January, three Kurdish women activists were murdered in Paris, allegedly by a Turkish Kurd now in French police custody, in a crime linked to terrorism although the motive of the killer remains unclear.
Disclosures about alleged U.S. "spying" on European partners sparked concern but did not have a major effect on long-standing and close transatlantic cooperation in combating terrorist threats.