ISTANBUL (Reuters) - Suspected Kurdish militants ambushed a Turkish military bus in western Turkey on Thursday in an attack which police said killed one soldier and wounded at least 11 people, adding to a recent upsurge in separatist violence. If confirmed as a Kurdistan Workers Party (PKK) attack, the ambush in the Aegean province of Izmir would represent a widening of the conflict with the PKK beyond its regular field of operation in the mainly Kurdish southeast of Turkey. The violence is a headache for Prime Minister Tayyip Erdogan as he seeks to limit the impact on Turkey of the conflict in Syria.