According to a Quinnipiac University poll released Tuesday, Clinton leads Obama, 53 percent to 41 percent, in Pennsylvania, which holds its primary April 22.

CNN reported the New York senator's lead in the Keystone State is twice as large as a similar poll showed in late February, but less than the 18-point gap she had over Obama, the junior senator from Illinois, a month ago.

Among white voters in the state, Clinton leads Obama by 28 points, compared to a 19-point gap in February. Among black voters, Obama leads with 76 percent support, up from 69 percent a month ago, the poll showed.

On the prospect of a joint Democratic ticket, 32 percent of Pennsylvania Democrats say they prefer Clinton on the top of the ticket, and 18 percent prefer Obama, while 43 percent say they don't want the two to run together, CNN reported.

The poll of 1,304 likely Democratic voters was conducted March 10-16, and has a margin of error of plus or minus 2.7 percentage points.