A U.S. Marine offensive in southern Afghanistan has too few Afghan forces for the task of winning popular support in the Taliban heartland and only four U.S. civilian experts, officials said on Wednesday.

Marine Brig. Gen. Lawrence Nicholson, commander of the Marine Expeditionary Brigade-Afghanistan, told Pentagon reporters only 650 Afghans had joined the 4,000 U.S. troops that swept into the Helmand River valley a week ago.

The region is the center of Afghanistan''s opium trade, which U.S. officials say bankrolls the Taliban insurgency.

The Marines have met light resistance from the Taliban, with only about 20 armed confrontations.

But Nicholson said many more Afghan troops were needed to build relations with local leaders and identify Taliban members believed hiding among residents.

"What I need is Afghan troops," Nicholson said in an audio link from Afghanistan. "I''ve got 4,000 Marines in the field and about 600, 650 Afghans. You can do the math."

"They understand those cultural sensitivities that we''re just never going to get," he added.