Obama made the comment aboard his plane Saturday night as he flew home from Chicago following a whirlwind tour of Puerto Rico, which has its primary June 1, CNN reported.

Obama criticized Clinton's efforts to convince top Democrats to allow the convention seating of delegates from Florida and Michigan, who were banned by the party because the states conducted early primaries.

"They weren't stirring it up when they didn't need the delegates," Obama said. "Let's not sort of pretend that we don't know what's going on. This is, from their prospective, their last slender hope to make arguments about how they can win."

Obama also took on presumptive Republican nominee and Arizona Sen. John McCain on military service and veteran's affairs, CNN said.

Obama said he would "cede to no one" on veteran's issues and looked forward to a "substantive debate" on the issue with McCain. McCain has said Obama "has less than zero understanding of veteran's affairs."