(Cover) - EN Showbiz - Katy Perry urged Americans to "vote early" with the help of a latex dress, designed to look like a ballot paper.

The pretty pop star wore the politics-inspired outfit to a rally-come-concert for US President Barack Obama, in Las Vegas yesterday.

In light of the upcoming elections, Perry showed her support for the current leader by performing and encouraging youngsters to vote.

"Don't wait. Go tomorrow. How many of you are 18 here? It's going to be your first time, right?" she told the 13,000-strong crowd.

The not-so-subtle dress boasted the words President of the United States across the top and a square box, filled in next to the names of Obama and Vice President Joe Biden.

The box next to name of competitor Mitt Romney was left empty as the songstress performed five songs, including her smash-hit Firework.

The screen behind Perry showed images of Obama and his slogan Forward, along with pictures of volunteers and supporters.

Obama took to the stage, thanking Perry for her performance and pleading with people for their votes.

The president also enjoyed some banter with 28-year-old Perry, joking the singer's grandmother almost got him into trouble with his wife Michelle.

"I've got to know Katy and she's a wonderful young lady," he gushed.

"And I can tell that part of it is because of her outstanding grandma Anne, a 50-year resident of Nevada. The only thing I have to say is Ann got some lipstick on me when she kissed me. Fortunately somebody wiped it off before Michelle saw it. I'm telling you, you're going to get me in trouble!"

Las Vegas was the third stop on a two-day tour, which has taken Obama to Iowa and Colorado and will see him finish up with Florida and Virginia. (C) Cover Media