Taliban fighters have entered the capital of Afghanistan’s Jawzjan province, a politician has said, as they seek to capture their second provincial capital in as many days.

Mohammad Karim Jawzjani said the militants had reached the city of Sheberghan but the Afghan government, while not denying this, insisted the city had not yet fallen.

Sheberghan is particularly important because it is the stronghold of Uzbek warlord Rashid Dostum, whose militias were resurrected to help the Afghan government forces.

Mr Dostum, a former army paratrooper, returned to the province last week after months in Turkey, where he is believed to have been receiving medical treatment.

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His spokesman Ehsan Nero told the AFP news agency that he was meeting senior officials to talk about security in Sheberghan.

Residents of the city said there had been heavy airstrikes and that the Taliban had freed prisoners from the jail.

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The militants have taken advantage of the departure of foreign forces from the country, quickly taking control of vulnerable districts and now turning their attention to provincial capitals.

On Friday, the Taliban took control of Zaranj, capital of the southwestern province of Nimroz, and the government said its forces were still fighting inside the city.

More than half of the country’s 421 districts and district centres are in Taliban hands and several of the provincial capitals are under threat.

The worsening situation prompted a warning from the UK government on Friday evening, advising Britons to leave the country immediately.

Many of the places under threat are remote but some are strategically important and would give the Taliban control of lucrative border crossings with Iran, Tajikistan and Pakistan.

Also on Friday, the Taliban fighters closed the border crossing with Pakistan at Spin Boldak, protesting against Pakistan’s demand that all Afghans crossing the border must have Afghan passports and Pakistani visas.

The crossing is important because it is one of the main routes for goods to be driven to land-locked Afghanistan from the Pakistani port city of Karachi.

By Saturday, more than 600 trucks, many carrying perishable food, were backed up in both countries.

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UK should ‘step forward’ to help Afghanistan

Meanwhile, the US has said the withdrawal of its forces from Afghanistan is more than 95% complete and will be finished by the end of this month, but the US Air Force continues to help Afghan forces defend Helmand and Kandahar in the south, in an effort to prevent a Taliban takeover.

In Helmand, provincial council member Nafeeza Faiez said Taliban troops are in control of nine of the 10 police districts in the capital city of Lashkar Gah.

Afghan commando forces and regular troops are trying to get the fighters out of the city but with little success, she said, adding that conditions for civilians are desperate.

Many are trapped in the city, unable to get supplies and unable to get to hospitals for medical help.