An Afghan official had earlier reported coalition air strikes against the forces of Amanullah Khan, who have been battling militia loyal to the governor of Herat province, strongman Ismael Khan, for several days.

"We did not conduct any air strikes in the Herat area today," said US military spokesman Major Rick Peat, adding that coalition patrol and transport planes were in the area.

"We are providing air support to the Afghan security forces, at the request of the Afghan government," he said.

Clashes have been raging in districts around Herat city since early Saturday morning and demonstrators had taken to the streets to demand the central government take action against militia threatening the provincial capital.

Speaking earlier on Tuesday, Herat police chief Ziahuddin Muhmoodi said the fighting had reached Adraskan district some 85 kilometres (52 miles) south of the city when the strikes hit.

"Amanullah Khan's troops were bombed by coalition planes," he said.

Sources in the central government said the attack had been ordered by President Hamid Karzai who had vowed to back Ismael Khan and defend the city of Herat against attack from Amanullah's forces.

"The attack on Ismael Khan is being considered as an attack on the central government. The government will defend its governor at any cost," Karzai spokesman Hamid Elmi told AFP.

A source close to the defense ministry said Karzai ordered the attack after Amanullah failed to pull back from Adraskan.

"Amanullah was told if he made a single step further towards Herat the government would take serious action against him. Amanullah right now is being considered as a rebel commander," he said.

Amanullah's forces captured and briefly controlled Adraskan earlier Tuesday, but lost control of the district in the afternoon after bloody clashes. They retreated after a truce was brokered.

"Based on the request of the central government, we handed over the control of Adraskan to the national army," Amanullah told AFP.

He also denied that his troops had been bombed by US-led coalition planes.

Meanwhile, the United States-led military coalition also said troops from Kabul were ready to be used if fighting spiralled out of control.

"The Afghan government naturally has the lead in this matter and is trying to resolve the situation peacefully," US military spokesman Peat told AFP in an emailed statement.

"However, they have positioned forces in the area, and are reinforcing them, to use should peaceful means fail."

United States ambassador Zalmay Khalilzad said the US had stepped in to broker a truce between the warring sides after four days of fierce clashes.

"The agreement has been made, has been honoured but I have indicated to Amanullah that any advance towards Herat to threaten the city is unacceptable," Khalilzad said at a press conference.

Khalilzad said it was unclear if the factional fighting was related to elections but that an investigation had been launched.

Herat was tense Tuesday and Governor Khan was seen distributing weapons to civilians at police headquarters and intelligence headquarters. Uniformed and plain-clothes armed men were stationed at every major intersection on Herat's streets, an AFP correspondent said.

The latest offensive caps a string of factional clashes between rival warlords battling for control of the western provinces of Herat, Farah, Badghis and Ghor in recent months.

Khan has ruled the city with an iron fist bringing peace and prosperity to its streets since the fall of the Taliban, but cracking down hard on his opponents.

WAR.WIRE