Ugaritic

ˀasr - prisoner, captive (DUL 114, Watson 2007: 79)

Since *ˀasīr- ‘prisoner’ is widely attested in WS, whereas Akk. asīru is probably an early WS loanword (Kogan2008b:105 and 110, with references), there is hardly an reason to postulate an Akkadian loanword in Ugaritic (Kogan 2015: 356).

PS
*ˀsr - to tie (Kogan 2015: 223)