Some 9,000 people attended the annual Jefferson-Jackson dinner in Des Moines to hear Sen. Hillary Clinton of New York, Sen. Barack Obama of Illinois, Sen. Joseph Biden of Delaware, Sen. Christopher Dodd of Connecticut and former North Carolina Sen. John Edwards discuss their platforms.

In various polls, Clinton has a double-digit lead over Obama, and neither of them spoke the other's name in their speeches Saturday night, The New York Times (NYSE:NYT) reported.

Clinton urged Democrats to refrain from attacking one another and to "turn up the heat" on Republicans.

Biden didn't take the offensive with his rivals and urged party members to choose a nominee with judgment and experience.

The sentiment was echoed by New Mexico Gov. Bill Richardson, who told Democrats to refrain from attacking one another, the Times said.

"It is critically important that Democrats not tear each other down," Richardson said. "I believe it's important to point out policy differences on Iraq, Iran. But it's important to remember the American people want a positive campaign."