(Wikipedia) - The 2010 Iran–Iraq border clash occurred on May 13, 2010, when Iraqi and Iranian border guards exchanged fire.
2010 Iran–Iraq border clash:
It was the first major incident between the two since December 2009, when Iran took control of a disputed oil well. The gunfight lasted 90 minutes and an Iraqi officer was captured. The clash was instigated in error, when Iranians mistook the Iraqi guard as members of an Iranian Kurdish rebel group.
The shooting took place in Shamiran, which is located in a mountainous region straddling the two countries' border.