The No. 2 commander of U.S. forces in Afghanistan says a planned troop withdrawal from the country will begin slowly, with the departure of about 800 National Guard troops later this month and some 800 Marines in the fall.

Speaking to reporters at the Pentagon by video link from Kabul Wednesday, Lieutenant General David Rodriguez said the troops will not be replaced. He said the drawdown will be carried out gradually as U.S. President Barack Obama has promised.

Mr. Obama announced last month that 10,000 U.S. troops will leave Afghanistan by the end of this year, with another 23,000 to depart by September of 2012.

In violence Wednesday, Afghan police said gunmen abducted 28 mine clearance workers in western Farah province.

Local police chief Sayed Mohammad Roshandel said the men were kidnapped in Bala Buluk district, after the gunmen set fire to at least one of their vehicles.

There was no immediate claim of responsibility, but kidnapping in exchange for ransom is a common strategy for local criminal groups and Taliban militants since the U.S.-led invasion in 2001 toppled the Taliban government.