Abu l-Qasim Al-Khu’i writes:

يَـجُـوزُ لِـلْـحَـاكِـمِ الـشَّـرْعِـيِّ (الْـمَـرْجِـعِ) إِجْـبَـارُ الْـكَـافِـرِ عَـلَـى دَفْـعِ الْـخُـمْـسِ مِـمَّـا أَخْـرَجَـهُ

“The legitimate judge (Marja’) may force the disbeliever (Kafir) to give over the fifth (Khums), from what he took out.” [Al-Mustanad Fi Sharhi l-Urwati l-Wuthqa, Volume 25, Page 36]