In the districts around the city, a particularly violent group of young Taliban commanders terrorise locals and exert parallel power.
The group has also welcomed Al Qaeda in the Islamic Maghreb, the affiliate of Al Qaeda in northern Africa, which has recruited child soldiers, established training camps and reached out to other militant Islamist organizations, including Boko Haram, a particularly violent group in northern Nigeria.
Several American and Pakistani officials said that the C.I.A. team with which Mr. Davis worked in Lahore was tasked with tracking the movements of various Pakistani militant groups, including Lashkar-e-Taiba, a particularly violent group that Pakistan uses as a proxy force against India but that the United States considers a threat to allied troops in Afghanistan.
Covering the fighting in Misrata, on Tripoli Street, a particularly violent stretch, they were among a group of journalists hit by mortar rounds.
Abd al-Rahman al-Zubeidy, political spokesman of Ansar al-Sunna, a salafist (purist Islamic) group with a particularly violent reputation in Iraq, said his organisation had split over relations with al-Qaida, whose members were mostly Iraqi, but its leaders largely foreigners.
But Sunni extremist groups have warned online that Ramadan would be particularly violent.
Studies by the Vera Institute of Justice, with offices in New York and New Orleans, and by other groups have shown the mentally ill aren't particularly violent or crime prone, Thierry said.
Among the users some ethnic groups, as well as the drug abusers, are seen as particularly violent.
Reports from Iran suggested that guards were particularly violent towards those prisoners accused of having links with the Iranian dissident group the People's Mujahideen of Iran (MEK) and held for many years.
Sunni extremist groups have posted warnings on militant Web sites that Ramadan would be particularly violent, repeating a well-established pattern.
