Four foreign troops have been killed by a roadside bomb in eastern Afghanistan, the Nato-led International Security Assistance Force (Isaf) has said. Isaf gave no further details about the incident in its statement. Most of the Isaf troops serving in the country\'s east, near the border with Pakistan, are Americans. At least 220 foreign troops have died in the rising violence in Afghanistan so far this year, including 57 in May, according to the iCasualties website. From BBC News