No. Only walls block line of sight.
Rulebook, page 19 wrote:
Line-of-sight: All ranged and melee attacks can only be performed against enemies within line-of-sight, which means that a line can be drawn from any corner of the attacker’s hex to any corner of the defender’s hex without touching any part of a wall (the line edge of a map tile or the entire area of any partial hex along the edge of a map tile, unless covered by an overlay tile). Only walls block line-of-sight.