BANGKOK (Reuters) -Thailand's military has closed border crossings into Cambodia to almost all travellers, including tourists and traders, citing security concerns as tensions between the two Southeast Asian neighbours remain escalated over a simmering border dispute. The deterioration in ties was sparked by brief armed clashes in a border area that left one Cambodian soldier dead late last month. Both governments have since announced measures designed to punish the other, including Cambodia's recent suspension of all Thai fuel and gas imports.