Jesus’ command to love one’s enemies is not a new teaching, but can be found in the Old Testament: “If thou meet thine enemy's ox or his ass going astray, thou shalt surely bring it back to him again. If thou see the ass of him that hateth thee lying under his burden, and wouldest forbear to help him, thou shalt surely help with him.” Exodus 23:4-5

Though the exact words are not stated here, the substance remains. A degree of love is extended to one’s enemies. This is in the same Old Testament containing the imprecatory psalms.

@irishpresby makes a good point on this in his book on imprecations