Afghan police said on Saturday that Taliban fighters had attacked a district capital for a second straight night and took 18 policemen prisoner, a day after detaining more than a dozen.
"Right now, the district headquarters is under the control of the Taliban, "said the officer, who declined to be named.
"The Taliban surrounded the district headquarters and captured 18 officers," he added.
Mian Nishin, in Kandahar province, was the scene of joint operations by Afghan and US-led forces early this week in which government officials said nine fighters were killed.
On Thursday, the Taliban had captured 11 police officers, the district police chief and a senior local government official in Mian Nishin.
The Taliban said Their fate would be decided by its leadership.
Taliban-linked violence has been surging in the south and east, raising fears for the security of parliamentary elections due to be held on 18 September. Much of the violence has been in Kandahar.
On Saturday, fighters attacked government posts in the Dai Chopan district of Zabul province, adjoining Kandahar, Gulab Shah Alikhail, a spokesman for the province said. He said four fighters were killed, but there were no government casualties.
Taliban spokesman Abd al-Latif Hakimi said the fighters had killed three policemen in the attack, which also killed one of their own.
On Friday, a roadside bomb exploded in neighbouring Helmand province, killing a soldier and wounding three policemen, including a district police chief.
On Monday, four US soldiers were wounded in an attack outside Kandahar city.
The Taliban have threatened more violence, while the government says the fighters are likely to step up attacks ahead of the elections.
More than 150 fighters have been killed this year, according to US military and Afghan government sources.
Dozens of government troops and 29 US soldiers from the 20,000-strong US-led foreign force have died since March, including 18 in a helicopter crash.
US-led forces invaded Afghanistan in 2001 due to what the US said the Taliban's refusal to hand over Osama bin Laden.