The Taliban have captured the key Afghan city of Pul-e-Khumri, 140 miles north of the capital Kabul, giving the insurgents control of a strategic road junction linking Kabul to the north and west, according to insurgents and local officials. Two officials in the city told the Guardian it fell to Taliban after heavy fighting on Tuesday, with officials and security forces abandoning their compounds. “Pul-e-Khumri fell to the Taliban, they are everywhere,” one official said in a phone interview during which the sound of heavy gunfire could be heard. “Taliban fighters broke through the frontlines in several directions during the afternoon. After heavy clashes, officials and security forces abandoned the governorate, intelligence and police headquarters. Heavy clashes are ongoing. We are deciding where to retreat now.” A Taliban spokesperson on Twitter also claimed the capture of the city, the capital of Baghlan province. Images on social media showed the Taliban’s flag at city gates and insurgent fighters inside the city. If confirmed, Pul-e-Khumri would be the eighth out of 34 provincial capitals captured by the hardline Islamist movement in less than a week. The city’s fall to the Taliban would be a massive blow to the Afghan government, threatening the remaining cities in the north of Afghanistan not already under insurgent control including Mazar-i-Sharif and Faizabad. Earlier on Tuesday, a senior EU official warned that the Taliban’s strategy in northern Afghanistan appeared to be to cut off the capital, Kabul, from forces to the north that could support it. The latest gains in the Taliban’s lightning advance came as a US peace envoy to Afghanistan warned the Taliban that any government that comes to power through force in Afghanistan would not be recognised internationally. The US envoy Zalmay Khalilzad went to Doha, Qatar, where the Taliban maintain a political office, to tell the group that there was no point in pursuing victory on the battlefield because a military takeover of Kabul would guarantee they would be global pariahs. Khalilzad’s comments came as the UN human rights chief, Michelle Bachelet, warned of a mounting campaign by the Taliban targeting current and former government officials and family members for “summary execution” and destruction of their homes and other property. According to the EU about 400,000 Afghans have been displaced by the fighting in recent months. Khalilzad and others hope to persuade Taliban leaders to return to peace talks with the Afghan government as US and Nato forces finish pulling out from the country. During the past two months the Taliban has rapidly expanded the territory it controls to about 65% of the country, including a large proportion of rural areas. A third of the country’s provincial capitals are under threat. The Taliban military chief released an audio message to his fighters on Tuesday ordering them not to harm Afghan forces and government officials in territories they conquered. In the nearly five-minute audio Mohammad Yaqoob, the son of the late Taliban leader Mullah Mohammad Omar, also told the insurgents to stay out of abandoned homes of government and security officials who had fled, to leave marketplaces open and to protect places of business, including banks. It was not immediately clear if Taliban fighters on the ground would heed Yaqoob’s instructions. There have been reports by civilians who have fled Taliban advances of heavy-handed treatment by the insurgents – of schools being burned down and of repressive restrictions on women. In a separate intervention on Tuesday, the UN human rights chief urged an end to the Taliban offensive on Afghan cities and said her office was receiving reports of possible war crimes. “The Taliban must cease their military operations in cities. Unless all parties return to the negotiating table and reach a peaceful settlement, the already atrocious situation for so many Afghans will become much worse,” Bachelet said in a statement. Bachelet’s remarks came as heavily armed fighters flooded into Farah city on Tuesday morning, with the Taliban announcing that its “special forces” had arrived in the city. The Taliban also posted pictures of its triumphant fighters standing in front of city’s main administrative building. Following a now familiar pattern, an official in Farah who spoke to the Guardian described a fruitless request for government reinforcements and desertions. “No help has so far arrived from Kabul, and we no longer expect them, if they wanted to send help they should have sent it,” the official said. “One of the intelligence officers switched sides last night and joined the Taliban with several of his men.” Another local official said earlier on Tuesday: “The Taliban have been active in outskirts of Farah city for weeks but they started their big assault last night and were pushed back. But now they are advancing again.” The official was surrounded by the Taliban in a government compound and the Guardian was unable to reach him after fall of the city. The fall of Farah followed the Taliban capture of Zaranj on Friday, which was followed two days later by the huge symbolic capture of Kunduz, a strategic city close to the border with Tajikistan and an important political and military hub. The group has also claimed Sheberghan, the capital of the northern Jawzjan province, Taloqan in Takhar province, Sar-e Pul in the northern province of the same name and Aybak in the province of Samangan.