WASHINGTON (Reuters) - A U.S. military offensive in southern Afghanistan could push Taliban fighters into Pakistan, whose troops are already struggling to combat militants, the chairman of the U.S. Joint Chiefs of Staff said on Thursday.
The comments by Admiral Mike Mullen raised the prospect that Pakistan, waging battles with militants who have forced about 2 million people from their homes, could face even greater turmoil in the months ahead.
The United States is pouring thousands of troops into Afghanistan this year to try to reverse gains by a resurgent Taliban, particularly in its southern heartland.
Mullen, the most senior U.S. military officer, said the United States had a clear national security interest in taking on the Taliban.
"They want Afghanistan back. We can't let them or their al Qaeda cohorts have it. We can't permit the return of the ... very same safe havens from which the attacks on 9/11 were planned and resourced," Mullen said.
"Yet we can't deny that our success in that regard may only push them deeper into Pakistan," he told the U.S. Senate's Foreign Relations Committee.
Senator Russ Feingold, a Democratic member of the committee, expressed concern about a possible spillover.
"We may end up further destabilizing Pakistan without providing substantial lasting improvements in Afghanistan," the senator said.
"Weak civilian governments, an increased number of militants and an expanded U.S. troop presence could be a recipe for disaster for those nations in the region as well as our own nation's security."
He suggested the presence of U.S. forces in Afghanistan after the September 11, 2001, attacks on the United States also pushed militants into Pakistan, where al Qaeda regrouped.
Mullen said he shared Feingold's concern, particularly that militants could cross from southern Afghanistan into the Pakistani region of Baluchistan.
"Can I ... (be) 100 percent certain that won't destabilize Pakistan? I don't know the answer to that," he said.
NO SUCCESS AGAINST OPIUM TRADE
Mullen said he thought a spillover could be avoided because both Pakistani and U.S. forces were aware of the possibility and were planning measures to prevent it.
Mullen also said the opium trade, which helps fund the Taliban, must be eliminated in Afghanistan and he acknowledged Washington and its allies had failed to tackle the problem.
"We have had almost no success in the last seven or eight years doing that, including this year's efforts," he said.
He said the United States and other nations had to step up efforts to provide alternative livelihoods for farmers who grow opium poppies.
The United States has 49,000 troops in Afghanistan and plans to reach a total of 68,000 later this year. Other nations, mainly NATO allies, have about 32,000 troops in the country.
(Editing by Peter Cooney)