By Daren Butler ISTANBUL (Reuters) - Turkish armed forces shot down a Syrian plane on Sunday that Ankara said had crossed into its air space in an area where Syrian rebels have been battling President Bashar al-Assad's forces for control of a border crossing. "A Syrian plane violated our airspace," Prime Minister Tayyip Erdogan told an election rally in **rthwest Turkey. Because if you violate my airspace, our slap after this will be hard." Syria condemned what it called a "blatant aggression" and said the jet was pursuing rebel fighters inside Syria. One plane entered Turkish airspace at Yayladagi, east of the Kasab border crossing, it said.