Suppose I insert into one of my papers a paragraph stolen from a paper by Quine, and I do so without reading the Quine paragraph. I then publish the paper. I have asserted everything in the paper, including the plagiarized paragraph. Suppose that the Quine paragraph contains a sentence that I know to be false—but I don't know that the paragraph contains such a sentence. Have I lied in that sentence? No, even though I have asserted something I know to be false. For imagine another possible world where the Quine paragraph contains only sentences that I know to be true. In that other world, my action (say, of pressing ctrl-c and ctrl-v) might well be exactly the same internally, and surely the difference between lying and not lying should be internal. After all, lying is a violation of sincerity.
If the above is correct, then to assert what one knows to be false is not the same as to lie, because one might not know what one is asserting.