On the red carpet, Nicole Kidman and Keith Urban look like the perfect couple, but behind closed doors, things aren't as picture perfect as they seem.

Nicole and Keith, both 49, are embroiled in the biggest fight of their 11-year marriage, and sources reveal exclusively to Life & Style that the couple is at odds over where to live.

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“Nicole wants to move back to Australia so they can raise their children among family, but Keith is opposed to leaving Nashville because his career is there,” says an insider. “They’ve been having this argument for almost two years now. It’s taking a toll on the relationship.”

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The pair's top priority remains their daughters Sunday, 8, and six-year-old Faith. Nicole believes Australia is the best place for the girls to grow up.

“Nicole likes the laid-back lifestyle there,” says a second insider. Says the first insider, “[She] wants her kids to have the same kind of upbringing she did.”

However, Keith, who moved to Nashville from Down Under in the '90s for his music career, believes he has to stay in the Music City to stay relevant.

“Nicole’s career doesn’t require her to live in the U.S. at all,” notes an insider. “She can just fly wherever she needs to film. But Keith tours at casinos and state fairs, and he performs at award shows, so he wants to stay in the States.”

Earlier this year, Nicole, who also shares kids Isabella, 24, and Connor, 21, with ex-husband Tom Cruise, hinted at the tension in her marriage when she revealed she gets anxious when Keith does not answer her phone calls.

"When people say they will do something and they don't. And I know it's terribly demanding, but I don't like it when my husband doesn't answer his phone," she told W magazine. "I have to keep calling and calling, and I get anxious. Does that make me high-maintenance?"

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