The fighting broke out between two commanders for control of districts surrounding Herat, the largest and most prosperous city in western Afghanistan, a spokesman for one of the groups said on Saturday.
"There were some military movements in Shindand district and Chisti district and roughly 21 people were killed on both sides," said Qari Massoon, spokesman for provincial governor Ismail Khan.
Troops loyal to Khan, who is regarded as the most powerful leader in western Afghanistan, clashed with forces under the command of Aman Allah Khan, from another tribal group.
The battle follows various outbreaks of violence between local leaders and US-appointed Afghan government forces in neighbouring Ghor province last month, in which three US soldiers were injured.
Fighting began at 2am (2130 GMT) in Shindand district and fighting was continuing for control of the airstrip, according to commanders from Ismail Khan’s group.
Among those killed were "Herat garrison commander Saif Allah and General Zakim Khan of the border brigade who supported Ismail Khan", said Aman Allah Khan.
"We have captured Shindand totally from Khan's forces and now the fighting is going on in Adraskan district," he added.
Shindand, about 660km west of capital Kabul, is a troubled district that has been controlled both by forces loyal to Ismail Khan, of Tajik origin, and Aman Allah Khan, a Pashtun.
The country remains fractious as
armed groups vie for influence
The two groups have had numerous clashes in the past two years.
Ismail Khan's forces reportedly attacked the outposts of Aman Allah Khan, triggering the fighting.
But the US-appointed Afghan government said its forces would come out in support of Ismail Khan if the fighting continued.
"Any action which would be taken would be in support of Ismail Khan," a defence department official said.
The official said Ismail Khan's troops were considered to be a pro US appointed government force, defending themselves against Aman Allah Khan's fighters.
"Any action which would be taken would be in support of Ismail Khan"
US-appointed Afghan defence department official
President Hamid Karzai's office issued a statement condemning the fighting as an "attempt to disrupt security ahead of the elections". It said "serious measures will be taken against the latest military operations".
"Afghans are preparing for the election process, which is making positive progress and this is the government's duty to prevent any kind of threats to the process," the statement added.
Local elections have been delayed several times, but the US-appointed Afghan government has vowed to continue.
Analysts believe the main driving force behind the move is more of a public relations exercise for the Bush administration prior to the US election. Afghanistan can thus be paraded as Bush's success story, in sharp contrast to what the US is facing in Iraq.
Parliamentary elections have, however, been pushed back to April next year mainly due to what the US appointed Afghan government calls "security problems".