Heavily armed Taliban fighters destroyed bridges near the central city of Ghazni on Saturday, closing the main highway between the capital Kabul and southern Afghanistan, officials said.
Sporadic clashes erupted between Afghan soldiers and Taliban insurgents who were trying to gain control over parts of Ghazni province nearly two months after being pushed back from the city by U.S.-backed Afghan forces, officials added.
Mohammad Arif Noori, the governor's spokesman in Ghazni, said fighting was ongoing and the Afghan army had deployed helicopters to prevent the militants from entering the city centre.
"We are fully prepared to attack them. This time the province will not fall into the hands of the Taliban," Noori said.
Five militants were killed as they were planting bombs on three bridges on the Kabul-Kandahar highway, Noori added.
The attack on Ghazni was a show of strength for the Taliban, underscoring how volatile the security situation remains two weeks before the parliamentary elections.
Polling has already been called off in Ghazni province after the Taliban overran it in August and besieged the city for five days.
That confrontation killed 150 Afghan security forces and 95 civilians dead, as well as hundreds of Taliban fighters, said officials then.
President Ashraf Ghani's Western-backed government pledged $20 million for relief and reconstruction of Ghazni after security forces defeated the Taliban fighters in that battle.
Afghan forces said on Saturday they were also fighting Taliban insurgents to retake a highway linking Ghazni and Paktia provinces. The Taliban took control of the arterial road in August and had imposed a tolls on civilians using the highway.
Rohullah Khalil Ughlo, an Afghan army commander, said 22 Taliban insurgents were killed and 17 were wounded in clashes to secure the highway.
"The operation will end soon and the highway will be open for traffic. People will not have to pay illegal taxes anymore," said Ughlo.
Meanwhile residents of Qarabagh district, 55 km (35 miles) south of Ghazni city, said the militants had set up checkpoints and were preventing vehicles from passing through several residential areas.