﴿ ۞ عَسَى ٱللَّهُ أَن يَجْعَلَ بَيْنَكُمْ وَبَيْنَ ٱلَّذِينَ عَادَيْتُم مِّنْهُم مَّوَدَّةًۭ ۚ وَٱللَّهُ قَدِيرٌۭ ۚ وَٱللَّهُ غَفُورٌۭ رَّحِيمٌۭ ﴾

“[But] it may well be that God will bring about [mutual] affection between you [O believers] and some of those whom you [now] face as enemies: for, God is all-powerful - and God is much-forgiving, a dispenser of grace.”

As far as justice and fair play are concerned, they will be given to everybody–whether friend or foe. But having friendships with those who are at war with one is not proper.