KABUL (REUTERS) - Taleban fighters captured the strategic Afghan city of Ghazni on Thursday (Aug 12), taking them to within 150km of Kabul following days of fierce clashes as the Islamist group ruled out sharing power with the government.

The speed and violence of the Taleban advance, including heavy fighting in their heartland and the second-biggest city of Kandahar, have sparked recriminations among many Afghans over US President Joe Biden's decision to withdraw US troops and leave the Afghan government to fight alone.

The gateways to the capital have been choked with people fleeing violence elsewhere in the country this week, a Western security source said. It was hard to tell whether Taleban fighters were also getting through, the source added.

With the last of the US-led international forces set to leave by the end of the month and end the United States' longest war, the Taleban now control about two-thirds of the country. On Wednesday, a US defence official cited US intelligence as saying the Taleban could isolate Kabul in 30 days and possibly take it over within 90.

Al Jazeera reported a government source saying it had offered the Taleban a share in power, as long as the violence comes to a halt.

Afghan government spokesmen were not immediately available for comment and it was not clear to what extent the reported offer differed from terms already discussed at stalled talks in Qatar.

Taleban spokesman Zabihullah Mujahid said he was unaware of any such offer but ruled out sharing power.

"We won't accept any offer like this because we don't want to be partner with the Kabul administration. We neither stay nor work for a single day with it," he said.

Under a deal struck between the United States and the Taleban last year, the insurgents agreed not to attack US-led foreign forces as they withdraw, in exchange for a promise not to let Afghanistan be used for international terrorism.

The Taleban also made a commitment to discuss peace. But intermittent talks with representatives of the US-backed government have made no progress, with the insurgents apparently intent on a military victory.

Route to Kabul

Ghazni, southwest of Kabul on the ancient route between the capital and Kandahar, was the ninth provincial capital the Taleban have seized in a week.

The militants on Thursday occupied Ghazni's government agency headquarters after heavy clashes, a security official said.

"All local government officials, including the provincial governor, have been evacuated towards Kabul," said the official, who declined to be identified.

Kandahar and other southern and eastern provinces bordering Pakistan have long been Taleban heartlands but they have made their biggest gains in recent weeks in the north. Even when the group ruled the country from 1996-2001, it never controlled all of the north.

There were heavy clashes in Kandahar. A Taleban commander told Reuters most parts of the city were in their control but fighting was still going on. In western Herat, a Taleban spokesman said their fighters had captured police headquarters.

Rallying old warlords

The Taleban said they had seized airports outside the cities of Kunduz and Sheberghan in the north and Farah in the west, making it even more difficult to supply government forces.

They said they had also captured the provincial headquarters in Lashkar Gah, the capital of the southern province of Helmand, a hotbed of militant activity.

Government officials there were not immediately available for comment. Fighting had also flared in the northwestern province of Badghis, its governor said.

President Ashraf Ghani flew to northern Mazar-i-Sharif on Wednesday to rally old warlords he had previously tried to sideline, now needing their support as the enemy closes in.

The Taleban risk isolating the country if they do seize overall control.

"Attempts to monopolise power through violence, fear, and war will only lead to international isolation," the charge d'affaires at the US Embassy, Ross Wilson, said on Twitter.

German Foreign Minister Heiko Maas said Berlin would not provide financial support to Afghanistan if the Taleban take over and introduce sharia religious law.

The violence has also raised concerns in Europe of more refugees arriving there.

The Taleban controlled most of Afghanistan before they were ousted in 2001 for harbouring Al-Qaeda chief Osama bin Laden.

A generation of Afghans who have come of age since 2001 worry that the progress made in areas such as women's rights and media freedom over the past two decades will be lost.

The United Nations said more than 1,000 civilians had been killed in the past month, and the International Committee of the Red Cross said some 4,042 wounded people had been treated at 15 health facilities since Aug 1.

On Wednesday, the Taleban denied targeting or killing civilians and called for an investigation.