WASHINGTON - US President Barack Obama poked fun at his likely presidential rival Mitt Romney and Republican opponents in Congress on Saturday night, including a dig at Romney's treatment of a pet dog, at the annual White House Correspondents' Association dinner.

The black-tie dinner, informally billed as the "nerd prom," is the biggest social event of the year for Washington media and gives presidents a chance to show a lighter side.

"I'm not going to attack any of the Republican candidates. Take Mitt Romney; he and I actually have a lot in common," the president said, telling the crowd of Hollywood celebrities and Washington power players that both men trailed their wives in national opinion polls.

Obama, who faces re-election in November, is expected to be matched against Romney, a multimillionaire and former Massachusetts governor.

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