News agencies cite authorities in Herat as saying as many as 21 fighters have been killed in the clashes, including top military officials loyal to Governor Mohammad Ismail Khan.
Amanullah Khan, an ethnic Pashtun commander in the provincial district of Shindand, said his troops have seized an air base in the district, some 660 kilometers west of the capital, Kabul.
An Afghan Defense Ministry spokesman, General Zaher Azimi, spoke to RFE/RL's Afghan Service: "According to our reports, the Shindand District...has fallen into the hands of supporters of commander Amanullah [Khan]. And now the fighting is continuing in Shindand airport.... There was also fighting in the Chesht District last night."
Abdul Wahed Tawakali, a spokesman for Ismail Khan, admitted there was hand-to-hand fighting at Shindand, but denied the air base had fallen.
Ismail Khan, a veteran of the 1980s war to end Soviet occupation, is a fierce critic of Afghan Transitional Administration Chairman Hamid Karzai.
Referring to fighting in Chesht District, near Ghor Province, Azimi noted that it remains unclear why the fighting broke out. "The Herat side [Ismail Khan] says this fighting is the initiative of Ghor's governor. But Ghor's governor denies the accusation and says this is an uprising of the people of Herat," he said. "We cannot say anything about these claims until our delegation visits Herat."
The Afghan government issued a statement condemning the fighting that is highlighting the fragile security situation weeks ahead of landmark presidential elections due in October.
Karzai said the fighting is "unlawful" and a violation of public security. He stressed that the attack on the
government-owned airport is an attack on the country's integrity and requires urgent action.
A U.S. military spokesman, Major Scott Nelson, expressed concern about the violence, and said U.S. forces are ready to support the government. However Nelson noted that there was only a small team of U.S. troops in Herat.
(RFE/RL's Afghan Service contributed to this report.)