About 20 suspected insurgents and one Afghan policeman were killed in a bloody battle in the mountains of southeastern Afghanistan, the US military said on Wednesday. Six American soldiers were wounded. Tuesday's clash, one of the deadliest in recent months, occurred in Dehchopan district of Zabul province, the US military said in a statement. It said helicopters and fixed-wing aircraft joined the fight against a group of about 25 insurgents. The statement said that the casualty figures were still preliminary. It reported five Afghan police officers were also wounded. Six insurgents were "detained and questioned". It said the wounded American soldiers were in stable condition, and two had returned to duty. The four others were to be flown to a US military hospital in Germany for treatment. The statement said the fighting began when gunmen fired on a group of US soldiers and Afghan police investigating a reported beating of an Afghan man. "The police and troops cordoned off the insurgent forces by use of small-arms fire and support from coalition fixed-wing and rotary-wing aircraft," the statement said. "Initial reports indicate approximately 20 insurgents were killed and one wounded."