A coalition base in Gardez in Paktia province came under rocket attack but there were no reported casualties or damage, US military spokesman Major Ralph Marino told reporters.

Marino did not say who was behind the attacks but similar incidents have been blamed on remnants of the ousted Taliban regime, their al-Qaeda allies or extremists loyal to renegade former premier Gulbuddin Hekmatyar.

Up to 1,000 Afghan soldiers supported by US troops and aircraft have been engaged for more than a week in a major operation against suspected Taliban and al-Qaeda bases in the mountains of Daychopan district of Zabul province, 300km southwest of Kabul.

US-led coalition Special Operation Forces and 10th Mountain Division troops backed by aircraft launched a fresh offensive in the Daychopan area Saturday, dubbed Operation Mountain Viper.

"The operation is going on," Marino told reporters at the coalition's Bagram Air Base headquarters, 50km north of Kabul.

He refused to give any further details but said Operation Mountain Viper was not limited to Zabul.

"Operation Mountain Viper is not just limited to Zabul but this is an operation anywhere in Afghanistan there is a presence of enemy," he said.

Zabul governor Hafizullah Hashim said Wednesday the suspected Taliban were surrounded and being bombed by US aircraft.

"Taliban caves were bombed early this morning (Wednesday). There are no reports of fresh casualties on either side," he told AFP from the Zabul capital Qalat, 60 km south of Daychopan.

"Some fresh Afghan forces have moved towards the caves from Qalat," he said.