1-Is it allowed any where in the world to take Interest from warring Kafirs in a territory of War or not?
2-And the surplus amount paid to a warring Kafir by a Muslim for the borrowed loan is Interest or no?
In the name of Allah, the Most Beneficent and the Most Merciful
According to the decisive decree, it is not allowed in Shari’a for a Muslim with a Kafir or a Kafir with a Muslim, to engage in Interest based transactions, neither in an Islamic territory nor in a Kufr territory or in a territory of War. The situation mentioned here is fallen in the similar category. Hence it is necessary to avoid and refrain from engaging in the aforesaid transaction.
Allah knows best.