INDIANOLA, Iowa -- Hours after Hillary Rodham Clinton urged President Obama to work with congressional Democrats to improve his free-trade initiative, Sen. Bernie Sanders slammed her for not taking a clear position on fast-track trade authority.

"It's not quite clear to me what Secretary Clinton is suggesting," Sanders (I-Vt.) told reporters here. "I am doing everything that I can to defeat fast track. . . . I am not clear, nor do I believe the American people are clear, as to what Secretary Clinton's position is. Is she for it or is she against it? Those are your two options. The president is for it. Most Democrats in the Congress are against it."

Sanders said Clinton's indecisiveness on fast-track legislation "is not leadership."

Asked by a reporter what Clinton is trying to do politically with her statements, Sanders replied, "Do I look like Hillary Clinton?"

Sanders's comments about Clinton represent perhaps his sharpest attacks in the intensifying Democratic primary race.