A roadside bomb killed five foreign troops in southern Afghanistan on Thursday, NATO said, less than a week after the coalition suffered its worst single loss in 10 years of war when Taliban insurgents shot down a helicopter. The NATO-led International Security Assistance Force (ISAF) gave no other details regarding Thursday's incident or the nationality of the troops killed. At least 50 foreign troops have been killed so far in August. Another foreign soldier was also killed by a roadside bomb in southern Afghanistan on Wednesday, ISAF said, giving no further details. Violence is at its worst in Afghanistan since U.S.-backed Afghan forces toppled the Taliban government in late 2001, with high levels of foreign troop deaths and record civilian casualties during the first six months of 2011.