Kautilya's Arthashastra 9.5.16

9.5.16

āhūya vā bāhyān ghātayeyuḥ //

When foreigners are abetting, the king should employ the policy of dissension and coercion. Spies under the guise of friends may inform foreigners: "Mind, this man is desirous of deceiving you with the help of his own spies who are disguised as traitors." Spies under the garb of traitors may mix with traitors and separate them from foreigners, or foreigners from local traitors. Fiery spies may make friendship with traitors and kill them with weapons or poison; or having invited the plotting foreigners, they may murder the latter.