Who is my brother?

Matthew 5:23-24:

So if you are offering your gift at the altar and there remember that your brother has something against you, leave your gift there before the altar and go first be reconciled to your brother, and then come and offer your gift.

Jesus didn’t say “unless they started it” nor “unless he’s being unreasonable.”  Nor even “you have something against your brother.”

Am I off the hook if the person having something against me is not my “brother”?  Jesus clearly defined “neighbor” as in “love your neighbor” to be everyone.  He didn’t so clarify “brother.”

Even if we limit “brother” to other Christians, we are still commanded to love our enemies and pray for those who persecute us.