Afghan security forces stand guard along the roadside in Herat. Photo: AFP
Herat - The interior ministry has also confirmed the fall of Ghazni.
The Taliban took over Herat, Afghanistan's third-largest city, on Thursday and also seized another key district capital just 150 kilometres (95 miles) from Kabul.
A senior security source from Herat told AFP that government forces and administration officials had retreated to an army barracks outside the city.
"We had to leave the city in order to prevent further destruction," he said.
A Taliban spokesman, however, tweeted "soldiers laid down their arms and joined the Mujahideen".
An AFP correspondent had earlier filmed the Taliban flag flying over the police headquarters in Herat, while the insurgents tweeted "the enemy fled... Dozens of military vehicles, weapons and ammunition fell into the hands of the Mujahideen".
Further details of the Taliban's presence in the city were not immediately available, but it has been under siege for weeks.
Herat - about 150 kilometres from the Iranian border - is home to veteran warlord Ismail Khan, who for weeks has been rallying his forces to make a stand against the Taliban.
Earlier, the interior ministry confirmed the fall of Ghazni, which lies along the major Kabul-Kandahar highway and serves as a gateway between the capital and militant strongholds in the south.
"The enemy took control," spokesman Mirwais Stanikzai said in a message to media, adding later the city's governor had been arrested by Afghan security forces.
Pro-Taliban Twitter feeds showed a video of him being escorted out of Ghazni by Taliban fighters and sent on his way in a convoy, prompting speculation in the capital that the government was angered with how easily the provincial administration capitulated.
As security forces retreated across the country, Kabul handed a proposal to Taliban negotiators offering a power-sharing deal in return for an end to the fighting, according to a member of the government's team in Doha who asked not to be named.
A second negotiator, Ghulam Farooq Majroh, said the Taliban had been given an offer about a "government of peace" without providing more specifics.
Authorities in Kabul have now effectively lost most of northern and western Afghanistan and are left holding a scattered archipelago of contested cities also dangerously at risk.