The funds in question will support the surveillance, reconnaissance and investigation of attacks, spokesperson Allison Hart said.
"We remain united and ensure that we are ready and capable of addressing all threats," she wrote in a statement.
Bulgarian Prime Minister Rumen Radev said earlier on Tuesday that US NATO aircraft had begun patrolling the Black Sea following a Bulgarian appeal for help in the wake of drone attacks.
According to EU foreign policy chief Kaja Kallas, Bulgaria and Romania have been subjected to six suspected Russian drone attacks in ten days, in what she called "a dangerous and unacceptable escalation".
She accused Russia of attacking Ukrainian grain exports.
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