WASHINGTON, July 23 (Xinhua) -- The U.S. Defense Department sees no possibility to send additional troops to Afghanistan before President George W. Bush ends his term due to constraints imposed by the Iraq war, Pentagon said on Wednesday.

    Despite repeated demand by the U.S. commanders for at least three more combat brigades in Afghanistan to curb rising violence, Pentagon spokesman Geoff Morrell told reporters that the Iraq war remains priority of the current administration.

    Even if President Bush makes decision to beef up troops in Afghanistan next year before he leaves the White House, "whether it is the three additional brigades that the commanders want I think is a question for the next administration," Morrell said.

    Bush is set to meet with Defense Secretary Robert Gates and other military commanders later the day to review the wars in Iraq and Afghanistan.

    The spokesman said that the meeting would also address the urgency for more troops sent to Afghanistan in near future.

    "Obviously we don't have the means to send three BCTs (brigade combat teams) to Afghanistan at this very moment, without making some very hard choices," he said of a more rapid reduction of the U.S. troops in Iraq or the mobilization of reserve troops.

    Currently, there are about 37,000 U.S. troops in Afghanistan, about one-fifth of the total 148,000 troops in Iraq.

    However, casualties of U.S. and NATO troops in Afghanistan has surpassed that of U.S. troops in Iraq in May, according to the military statistics.

    Gates earlier said that the Pentagon was looking for ways to send additional forces to Afghanistan "sooner rather than later."

    U.S. military's Joint Chiefs of Staff, Michael Mullen also warned after a visit to Afghanistan that the insurgency in the country have grown stronger with better training and increasingly sophisticated tactics.