The top U.S. military officer says he is concerned about the security situation in Afghanistan, and the United States will not be able to do much to help until it can reduce its troop presence in Iraq.

Admiral Mike Mullen told a Senate committee Thursday, continuing violence in Afghanistan has him worried.

"I'm deeply concerned," said Admiral Mullen. "The Taliban is growing bolder. Suicide attacks are on the rise, and so is the trade in illegal narcotics. In this economy of force operation, we do what we can. But doing what we can in Afghanistan is not doing all that we should."

The admiral says that is not likely to change until further U.S. withdrawals from Iraq make more troops available for Afghanistan.

"Requirements exist there that we simply can not fill, and won't likely be able to fill, until conditions improve in Iraq," he said.

Admiral Mullen says the top U.S. military officers, who head the four armed services, agree that adding troops to the NATO mission in Afghanistan will be their next priority, once they get some troops home from Iraq. But he says the service chiefs also want to give the troops more rest between deployments, and more training on skills other than counterinsurgency.

At the NATO summit in Romania last week, President Bush told his colleagues the United States will send more troops to Afghanistan next year - a promise he made even though his term in office ends in January. At the Senate hearing Thursday, Defense Secretary Robert Gates said he encouraged President Bush to make the statement, and has "confidence" further U.S. withdrawals from Iraq next year will make it possible to send more U.S. troops to Afghanistan. But he said that does not mean the United States will fill all of the needs the NATO commander has identified, which amount to more than 10,000 troops.

"We were very careful in Bucharest that the president not make a specific commitment or a specific period of time when additional U.S. forces might be available," said Robert Gates. "So, I think it's an open question how much of that three-brigade request the United States would be prepared to fill, or could fill. And that decision will almost certainly need to be made by the next president."

The United States just sent 3,200 Marines to Afghanistan, including a highly capable expeditionary force and some trainers for the new Afghan army. That brings the total U.S. contingent to 28,000. But senior U.S. officials have said they do not plan to replace those Marines when their tour of duty ends in October.