Tajikistan said that frontier troops from neighboring Uzbekistan crossed into its territory this week, prompting an exchange of gunfire in the latest of a series of such incidents in Central Asia, AP reported. The border service said Friday that an Uzbek soldier on horseback was spotted on Tajik soil filming footage on a mobile phone. It says an attempt to detain the soldier elicited a volley of gunshots from Uzbek troops. In a separate incident, Tajik authorities say that one of its citizens was forcibly detained by Uzbek soldiers on Sept. 1. His current whereabouts are unknown. Unclear border demarcations among ex-Soviet Central Asian republics have been cause of recurring tensions. Two border guards, from Uzbekistan and Kyrgyzstan, were killed in July in a clash that escalated from a local dispute.