WASHINGTON - Admiral Mike Mullen, chairman of the US Joint Chiefs of Staff, said Tuesday that the US military is bracing for a tough year in Afghanistan with potentially significant losses.

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Mullen made the comments as he visited US bases in Afghanistan, according to the American Forces Press Service affiliated with the Pentagon.

"We're going to have a very tough year this year. I've been very straight with the American people on that," he told reporters traveling with him to Afghanistan and Pakistan.

"I think our losses, which were significant last year, will be significant this year as well," he said.

The Obama administration planned to start withdrawing troops from Afghanistan in July, with the goal of handing lead security responsibility to Afghan forces by the end of 2014.

Still, Mullen added, it will be a tougher year on the enemy.

"The Taliban had a really tough year last year, and will have a tougher one this year," he said. "I think we'll know a lot more as to where this all stands ... at the end of this fighting season."