"... are now on the mercy of ..."

[Odessa Dawn]

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"And on 1967, the Arabs led by Egypt under the rule of Gamal Abdul Nasser, went in war with Israel and lost more Palestinian land and made more Palestinian refugees who are now on the mercy of the countries that host them."
More: Arab Spring and the Israeli enemy

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Can I use the preposition on with the underlined idiom instead of the preposition at? Thanks in advance.
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at someone's mercy
at the mercy of
at the mercy of
be at the mercy of sb/sth

 

[Rover_KE]

Yes.

 

[SoothingDave]

"On the mercy of" sounds weird to me. As does "went in war with."